Enhance MolMole downloader with metadata integration

[dmzio]

Summary

• extend the downloader to pull MolMole repository annotations, copy MOL files, and populate labels.json with structure metadata
• update the evaluator to consume multiple ground-truth SMILES values from the enriched labels
• expand downloader and evaluator tests to cover the new metadata workflow and alternative SMILES matches

Testing

• uv run --no-project --python .venv/bin/python -m pytest

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https://chatgpt.com/codex/tasks/task_e_68ffedac29a8832fb5a74371eac0e7d6