draft: Support RDKit chemistry answer formats

[danecor]

Summary

• add rdkit_chemistry answer_format parsing for fmt_00 through fmt_30
• preserve legacy use_box_format fallback while giving answer_format precedence
• document answer_format and add targeted extraction/reward tests

Validation

• uv run --extra dev pytest resources_servers/rdkit_chemistry/tests/test_app.py -q
• uv run --extra dev ruff check resources_servers/rdkit_chemistry
• uv run --extra dev ruff format --check resources_servers/rdkit_chemistry

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