feat: add MIMIC-IV OMOP test support (closes #13)

[rafiattrach]

feat: Add MIMIC-IV OMOP test support and validation

This PR adds the MIMIC-IV OMOP demo dataset to the test suite and verifies that croissant-maker correctly generates metadata for it "out of the box".

Changes

• Added MIMIC-IV OMOP demo dataset (v0.9) to tests/data/input/.
• Added new end-to-end test case test_mimiciv_demo_omop_generation in tests/test_end_to_end.py.

Results

The existing CSVHandler successfully processed all 22 CSV files in the OMOP export without requiring any code changes.

• Correctly identified file structure, row counts, and columns.
• Properly handled and skipped empty files (e.g., provider.csv, note.csv) to avoid creating empty RecordSets.
• Generated valid Croissant JSON-LD that fully complies with the v1.0 spec.

Related

Closes #13

[tompollard]

Very cool, thanks @rafiattrach!