fix(tests): make cellxgene repr_dict robust to a spurious None layer key (#265)

[Elarwei001]

Resolves #265

Summary

tests/test_cellxgene.py::TestCellxgene::test_cellxgene_adata started failing on py3.12/3.13 (it is skipped on py3.14, where cellxgene-census has no wheel) due to upstream drift, not any change in gget: cellxgene-census's get_anndata() now returns an AnnData whose .layers exposes a spurious None key. The test's repr_dict() helper turned that into "layers": [None], which no longer matched the stored expected structure.

Fix

repr_dict() now ignores None keys when summarising an AnnData's structure, so the comparison stays on meaningful (named) elements and is robust to this drift. The test_cellxgene_adata fixture is left unchanged (no need to hard-code the spurious [None]). This is a test-only change — no gget/ code is touched.

Testing

Unit tests (offline, no cellxgene-census needed):

• new TestReprDict::test_repr_dict_ignores_none_layer_key — a fake AnnData with a None-keyed layer must not surface layers, while named obs/var elements still do. Runs on every Python version, so it guards the fix even where the live Census tests are skipped.

Live tests (test_cellxgene_adata etc.):

• unchanged; they exercise the real Census on py3.12/3.13 and should pass again now that repr_dict ignores the None layer. I could not run them locally (local env is py3.14 without cellxgene-census), so CI on this PR is the confirmation.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.31%. Comparing base (e43a804) to head (0bd7c3d).
⚠️ Report is 2 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #266      +/-   ##
==========================================
- Coverage   56.70%   56.31%   -0.40%     
==========================================
  Files          29       29              
  Lines        9392     9392              
==========================================
- Hits         5326     5289      -37     
- Misses       4066     4103      +37     

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