Add StateBench dense-100m C++ curriculum (part 2)

100M verified state episodes packed into 25M rows, generated by the audited C++20 batch pipeline.

data/dense-100m/validation/part-00001.parquet

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:27ddaf573f9768ec7732529890b7c7cea88770f329b9f1e0d16d5fa6cf1ab7f6
+size 101814309