Address remaining style issues

[tsalo]

Changes proposed:

• Let Cursor address remaining style issues flagged by ruff.
• Add Python 3.14 to tox matrix.
• Fix failing tests.
• Fix failing RTD build.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 21.42857% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.52%. Comparing base (dbfe3a6) to head (2d5ac25).

Files with missing lines	Patch %	Lines
src/modelarrayio/fixels.py	12.50%	7 Missing ⚠️
src/modelarrayio/voxels.py	40.00%	6 Missing ⚠️
src/modelarrayio/cifti.py	20.00%	4 Missing ⚠️
src/modelarrayio/tiledb_storage.py	0.00%	4 Missing ⚠️
src/modelarrayio/h5_storage.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
- Coverage   39.62%   38.52%   -1.10%     
==========================================
  Files           8        7       -1     
  Lines         954      937      -17     
  Branches        0      137     +137     
==========================================
- Hits          378      361      -17     
+ Misses        576      550      -26     
- Partials        0       26      +26     

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