Make info gene test tolerate missing enrichment

[daveringelberg]

Summary

• make test_info_gene use a custom assertion for gget info DataFrame output
• keep Ensembl-derived fields strict while allowing UniProt/NCBI best-effort columns to be absent when upstream enrichment is unavailable
• still validate UniProt/NCBI enrichment values when they are returned

Fixes #267

Tests

• python -m pytest tests/test_info.py -q
• python -m ruff check tests/test_info.py
• python -m ruff format --check tests/test_info.py

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.42%. Comparing base (e43a804) to head (127523d).
⚠️ Report is 2 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #268      +/-   ##
==========================================
+ Coverage   56.70%   57.42%   +0.71%     
==========================================
  Files          29       29              
  Lines        9392     9392              
==========================================
+ Hits         5326     5393      +67     
+ Misses       4066     3999      -67     

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[daveringelberg]

CI failures appear unrelated to this PR: test_info_gene passes on all Python versions, while the visible failures are in test_cellxgene.py::TestCellxgene::test_cellxgene_adata. Happy to rerun or adjust if needed.