croissant: drop content fields so records-generation test streams cleanly

croissant.json: cumulative update (RAI dual keys, citation, new title/authors) (#12)

croissant: dual rai: prefixed + unprefixed RAI keys for validator compatibility (#9)

croissant.json: unprefix RAI fields, add @context aliases (NeurIPS RAI compatibility) (#8)

croissant.json: split aggregated recordSets to one per fileset (source cardinality fix) (#7)

Update Croissant 1.1 metadata: fix forbidden chars, paths, recordSet IDs (#6)

Add Croissant 1.1 metadata (croissant.json) (#4)