Fix CoNLL-U parsing bugs and improve metadata fidelity

Critical fixes:
- Fix double equals parsing bug (Gloss==POSS.1SG.NOM now preserved correctly)
- Preserve duplicate metadata keys (1,323 sentences across 14 treebanks)
- Handle empty metadata values and keys without values
- Bypass conllu library bugs with raw TSV and comment parsing

Improvements:
- Add comprehensive documentation (CONLLU_PARSING_ISSUES.md)
- Merge validation scripts with -vv option for detailed diffs
- Reduce diff context to 1 line for cleaner output
- Regenerate all 506 parquet files with fixes applied

Validation results:
- 47,131 test sentences: 100% perfect match
- bej_autogramm: 763/763 sentences verified (double equals fix)
- be_hse: 25,994 sentences, duplicate keys preserved
- Overall: 100% linguistic data fidelity, ~99.98% metadata fidelity

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

parquet/abq_atb/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:8de02a331245ade1c8b782fb9be4dedfb5dff8f718a280b3cf501fd117c49e0f
-size 42086
+oid sha256:32f0688797ec589d910747e1d5eb3b55021c5c442ebce9ad81425c8d55f160f6
+size 62925

parquet/af_afribooms/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:9286aaf7fbbf3dd58909eb2a8f6a268cdd009699a1661b40b0c3e7a5633861b0
-size 91924
+oid sha256:56bcf4d4f1c8f744134895c0afb48b7a5738e3830bddc5a9e27feb8e916091e0
+size 95425

parquet/af_afribooms/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:c4918c933ae0aca2918faaf588aa4aed024e3b9e55441b99f41690f1aaad745f
-size 164513
+oid sha256:f457fbad931caf55ab271e855aff42c79f9489b183ba7b5373bc4a8a9e1c8abe
+size 170408

parquet/af_afribooms/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:bc416821ec44c97f64b93aecae8ade7fec6a38697301d8feeb7f5beba8bc09dd
-size 458494
+oid sha256:c4dcbd01956b964acfe86698d4929e99af6de5c4e1af311eafc5b1a8ede83a80
+size 475968

parquet/aii_as/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:9598496348c4ab199417dace88bf54a2b50a8ab804bee68132f7fde4d2c42839
-size 23890
+oid sha256:84d5d85194626d4518bebd04f179cc83e5c82501c559e806a3197cd9bd717ab8
+size 25003

parquet/ajp_madar/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:410e64387b46598f7fe8704d481037242f41200da0b135db95cb929ae8eb4ab2
-size 27330
+oid sha256:cf342a4bb84045aab0128a5a94c09647ea38df030ce336ba2978a203a771831e
+size 28381

parquet/akk_pisandub/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:2e8deb223d124ad20db43527fd0bc9a347cf07d31c93ed95325facc3d19f2b0b
-size 45556
+oid sha256:c47bd7273a5c4fd0c06fe185199b854fb15622602d0008bf1d3b82fe93a37ddf
+size 53095

parquet/am_att/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:58d80b5da53899bdd2c401080b5163ae44c541cf8edfc2ad6257832d7b041b95
-size 199824
+oid sha256:e995cbc23b71d5320b6032ff0dd4eae0e48a78a4a979bef9c71d236355a72dd3
+size 237170

parquet/apu_ufpa/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:b552245edfbbee7eada762da352a997e10019e6cdb34910bca599aef21d7441e
-size 41352
+oid sha256:867771018ff54e41dfbec6693b3067d4a634c212dd0055d099ca17b9e61365b9
+size 62282

parquet/aqz_tudet/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:b33936c2b73f965d6f76aa904164b430e0a596632e9a81fa044a93b6a59b0b8a
-size 36999
+oid sha256:1b2c39d00427c65afbffe922572b106d72564e32ac428ea1a3474e80bf2281d9
+size 48779

parquet/ar_nyuad/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:0b285cd8ae80f8d934c771f8591a3b49b24007baf63a4d8dad551514833f785b
-size 455764
+oid sha256:71c3d83a277b738fd16ca2e6df9af91af773e03110d36da7ba7f0ee183954776
+size 455832

parquet/ar_nyuad/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:abbf287008519d48476ed831bb8245eeef24879363b12b813024fdc0928c60f3
-size 453598
+oid sha256:d09929c394426491968e9cd5c95d9aadfa7a38ee610a49c0d718c7ba2625de10
+size 460700

parquet/ar_nyuad/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:ca6d6d19bc08f43262740d05b94522cd0276937b06765360fdea8bfbb0b8141a
-size 3406999
+oid sha256:402b0c5270ef832f91f5b8451fdfb2db29d9a37d2d11afe7ba3e63ea0e665917
+size 3438256

parquet/ar_padt/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:c7c36219825ad815c713d373aef97dc2a1590a129782c99a89777a43315d5832
-size 1032235
+oid sha256:e4be5e9d4dcfc346e91f1b075b4fc3cdd17e8ea5bb7b103afefd5d67f2959f93
+size 1102296

parquet/ar_padt/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:0c3dcd7cf81c7f53e623ae89825aa62912852ffe787eec2c41145551b5ac8630
-size 983165
+oid sha256:6a3951b97259de8837b6595905566d67648d06a1b58110de927059515478f1f3
+size 1047007

parquet/ar_padt/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:d686341c8a384bbc0ff0f28099aa9fcc3b9ca9c6bc46ade6bb16898286e6c5f3
-size 9152014
+oid sha256:d9501b69823e77246371b9ebdfda3acf0a967f413f5a02ccd2e969ee9368814f
+size 9681738

parquet/ar_pud/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a97646566422f6d4f9b949962552b9ff284ce06dc08f7a1f538d44b89125491b
-size 472425
+oid sha256:e5545996d0ee285b44584f046d093fd5f477101e6dadcb267ad35c2dbd0ce378
+size 675931

parquet/arr_tudet/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:7af2c46c9ed785eea6aa5be67a11ae2c6fcb19165c6a0bee65dfdbf64d406747
-size 50766
+oid sha256:199e7d163897b006c66076fd539ad9fe74db762270bbcabfbabcf6eecf851e2e
+size 67869

parquet/be_hse/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:d3221a3225d9b0b39dc9ebdadf1d819f941cfec08f5ea992f84099e1fa345833
-size 408517
+oid sha256:54aeb4457a79d069aee086aa526c2ae06f6033061c5d7b1234d876f18a0bd9e6
+size 424218

parquet/be_hse/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:8bf1a4508bb5ab03cca854a3356d041fc24462e095728dfaed9220ff34868e0d
-size 395921
+oid sha256:127fa6c907be7b28208073bac36b1a55abce068381be00017ee7436691e8b247
+size 401477

parquet/be_hse/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:7454e4609a8ec07aeeb979ead4ce6773497f3edf2a1b937123337cf49bc35603
-size 5723698
+oid sha256:fd2d6b3161b3bc81ae953817a936a7ead96de41140d32cb850913bcb64edca0a
+size 5967300

parquet/bej_autogramm/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:59120773c7ab87a89d8a049ae05f032b00ebae886f359cb5d6f8ad96cdfae607
-size 426328
+oid sha256:85f2c03d3a0707c3ce69564b2ca3ea25e16b67ceba539599c408781adb96846f
+size 521309

parquet/bg_btb/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:8eb4b2b9dd3809b30210ec94c85840fd26d9c540baca50977f504f0571ca71cb
-size 390737
+oid sha256:162bcbe6de9bcbdd85a95b9b2c504538d7467653d7f5664a0e099fb7b74f1e28
+size 390518

parquet/bg_btb/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:6c46114fd5b02c99a3a82cdf8d6a1c30b8421ce49d415e4065ea6f9ff16578dc
-size 385319
+oid sha256:eefc36ad88c96270e65bb94c690295daca14ffd489178f82203db20220288227
+size 386112

parquet/bg_btb/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:585008a9ebfd23bf06895174823f5e9ad55ca705bbae548a8dea59da49f13c0c
-size 2466764
+oid sha256:401519af05aae6651870312d614e84aae901322f6eee70b7389f6e7281d0d5bf
+size 2460026

parquet/bho_bhtb/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:0034f69a91eecd2f6ba2b58a817d8afeb556d8f7a28e8509b1b916dab24fe408
-size 150097
+oid sha256:5aaa4efe62468d9e46521bb8ca69c447023342b9498c0339295014ff8c2255fc
+size 173052

parquet/bm_crb/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:2fc35bd5cdaee737276b59dcdbbabd44bf948377ee0c95e1caefcf9e54f1f7e0
-size 186321
+oid sha256:fd0952bcd02df85ba2cb913504def1b0a1706926045aaa569f143b7cce0c09c8
+size 188313

parquet/bn_bru/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:eef00e81c51332203e057e6a7c7eb513109b9c77280698035b04a5d5d7eb2ce6
-size 21602
+oid sha256:b439b9968146156f7968a154debc7fa58e5cda5a8ab38c99335c54b49edb342b
+size 25725

parquet/br_keb/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:bd10b4acf18d6aabce54064a45d892ee06fdc9214267a2cd645c5f409f607a2f
-size 167948
+oid sha256:9b294cc116e301f09c46e80635fa35f1c868dc752fe0c86d833ce03857ce13e3
+size 239911

parquet/bxr_bdt/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:bbc627dc590e0e0832edfb237daa1a4ca913333cf498b772563f8888f7a25037
-size 216034
+oid sha256:44f2e3a13a44583e71745314d74ccac371d3d1f9a890cba8401052c8d550e6e1
+size 217993

parquet/bxr_bdt/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:2e352eeb469d162a45a744175ddecf18609b48321238d973be203ddb1089f4cc
-size 17384
+oid sha256:f275c9a34e17db3bfb0864f193cc1224b947ce9083f9dd2d6dbbb2ce7f5f8b38
+size 19477

parquet/ca_ancora/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a2b86d65bc766cf8790f91725d10172bf68d8aeeacc9f2d7d8d77d6b1719952a
-size 1141973
+oid sha256:1ff785dd121d4f6f81f2464d6fba008fa0cb4b2ad737e7cea4752b2eb9ad8959
+size 1156119

parquet/ca_ancora/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:fdb6b891cc41267f5c1e33c787b836e0da3f31fbcd32258488459392583a0974
-size 1175875
+oid sha256:bb7d1d322d2396b5a5dfbc0103e9322899c8638df7d1d29540e51ca0e81fdca5
+size 1190804

parquet/ca_ancora/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:08721cd852fb198afc4dfaa735defd58f762fa2c881157af31f580a4b9d3daa9
-size 8125975
+oid sha256:0f33c602a6ecdf6908611d670b7d45f97155ce3e0b15afce8fcdb4e42c069c6c
+size 8226723

parquet/ceb_gja/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:058cfd6bedbc8906571482025a23c5b32d0db0843bba7b19d6427e35a2b49600
-size 41697
+oid sha256:7596374d2a517879c16da1411b4b6bda9384477628e569b9a51b3a7e0b7ddce7
+size 52497

parquet/ckb_mukri/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:cf6899b511f32fcab2dfe6e54c4931afc312db96f87297cab19ab8cf16991d26
-size 14725
+oid sha256:ff4346fa44d0b3b57384c95798ba2dac0e6f6b9f67374952940d097cf806fa3f
+size 15782

parquet/ckb_mukri/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:f5e251daa5b9305aea0c06aa8bbc9bf9c53a36664581634dcd6135cd7a4eb85c
-size 15335
+oid sha256:1b03e204db1c22b8ce72c1da2f4e625618fd4a2f4c925544e1ec7e3997292ca4
+size 16388

parquet/ckb_mukri/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:bf3ea80754b4318ce9205cfd55ef91118a0fbf868ab523d5dfb7d013e25fcf47
-size 22948
+oid sha256:1b784332a2f7d5d56de1cf51cdb8dc8b8e37656e30e884b78d7adff301efac19
+size 23985

parquet/ckt_hse/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:247cc7b360fc0fd995488d2a1b26142b2781034bfaf26cd656b0f66f9bc3e070
-size 186589
+oid sha256:9851a076597a88c741c84a4f1a5eaa567f5f1a4b4f611c6eec32c2d3e15f0720
+size 306267

parquet/cop_scriptorium/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:036b9d0bad4d947d7a1bc04b7baf6f60adfdfef253e5b1e9fd985099715b1efc
-size 205866
+oid sha256:de6c2bce883226de85ec0ba07a09e1a3ab35506d8f90298330e17fa437b5d5b5
+size 227494

parquet/cop_scriptorium/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:30d6a0378e1ddf94faab9172e9ffae540d809e9444902b556992dc742c58cab9
-size 198301
+oid sha256:252cde61b95f697a91c4c3ce515c56adf4d1ee6ab5b4ad95206a7c6d0486b78c
+size 217521

parquet/cop_scriptorium/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a7dd078f1188b2cbb4b15c99835c956c0fd0cf3c8da216cee4ddc485430e30ce
-size 610016
+oid sha256:9f8b64686bb84894cbf63ca9438c9386c60155868d08939d101833805bb7b48b
+size 677156

parquet/cpg_amgic/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:992dd34d8deb480bc8e9d2f201fde0c8eca9142b044a58aa3d1343c322b8acf2
-size 25997
+oid sha256:1cfa4f9fa69acc073ca79718e5a41419c2f3d156d4f68e350f4eb8b31de5116b
+size 32796

parquet/cs_cac/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:a570bebf7c74b3f654d718e226ce8ce4d3afcd236dde831599ec6b757889ca82
-size 288523
+oid sha256:3e2466a3446b5b04a1b7c59efb67c17088e84d30e245f4ebb70e0e09f84b74ba
+size 291165

parquet/cs_cac/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:963e610d69f2594820a6d7f57d5e3e70ac16bf011d2bef88e77ae6f82b463f9d
-size 288899
+oid sha256:7262678f160ababa6b7551fcfbf666526092fd091ef1698e55a4d1703e0b2d67
+size 291835

parquet/cs_cac/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:9065696e172ee8e3b6e18fe903dbe4bea2a49e96cc6044512e5c56f73c62356b
-size 9216544
+oid sha256:4be85764a2cfb81e9d3d9d990c4d649150b3a699e2c8013cc54368e8f0e59604
+size 9280973

parquet/cs_cltt/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:46e0a74b045e0b84457618ed45f21c84913a1259512fa2491e843a62f27926b6
-size 235623
+oid sha256:7ca6b456efd4c66c0a3ecbfaba57d95d8234262db1c84667e0128c96404fbcc2
+size 237494

parquet/cs_cltt/test.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:40f001317f633141950b48e11d425b1438d24aecd6de399c1dd2828af0cbb17a
-size 237646
+oid sha256:06ba30af79eee3fd09700956a0c20cfdb158200963e731f2dac843c96da28499
+size 239968

parquet/cs_cltt/train.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:81fcf01d9a30761e72252808b835ab7fa09f711ede894e1a2044a82d2d7eadb9
-size 276373
+oid sha256:0a1ae897bfd2bcd409abf6bfdecdc87fc2136d506cb8fa537e932becfd51afbb
+size 281020

parquet/cs_fictree/dev.parquet

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:f8082cb7ef7845df14cec89173957d41273435f61081eed4395f1e092eae31c9
-size 383984
+oid sha256:9e27671032474d7325f9605298779fb7e3b49913510cd91af6e7fc5c28be0aab
+size 393699