Keep category colors in sync when filtering tables

[syahra712]

Closes #1271

Following the suggestion in the issue: _inplace_fix_subset_categorical_obs already restores the original categories of a filtered table, and it now also restores uns["<column>_colors"] from the original table. The colors are only copied when the original list has one color per category, so a palette that was already out of sync is left alone.

This helper is shared by the joins in relational_query.py, so the fix applies to every path that goes through it: bounding_box_query / polygon_query with filter_table=True, and the join functions.

The test reproduces the issue's example: three cells of types A, C and B, with B outside the query box. Categories stay ['A', 'B', 'C'], and the colors are again ['red', 'green', 'blue'] instead of ['red', 'blue'].

LLM disclosure (scverse AI policy): Claude Opus 5.5 via Claude Code was used to write this change; the new test and the existing query/operations tests (517 passed) were run locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.42%. Comparing base (4d19f7d) to head (2efdf22).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1277   +/-   ##
=======================================
  Coverage   91.42%   91.42%           
=======================================
  Files          53       53           
  Lines        8381     8388    +7     
=======================================
+ Hits         7662     7669    +7     
  Misses        719      719           

Files with missing lines	Coverage Δ
src/spatialdata/_utils.py	85.88% <100.00%> (+0.60%)	⬆️

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