Fix render_shapes crash when obs index name conflicts with column

[timtreis]

Summary

• Workaround for upstream spatialdata bug (join_spatialelement_table crashes when obs index name matches an existing column spatialdata#1099) where join_spatialelement_table calls table.obs.reset_index() without handling the case where the index name already exists as a column
• Affects Merfish data where EntityID is both the obs index name and a column, causing ValueError: cannot insert EntityID, already exists when calling render_shapes(color=...)
• Temporarily drops the conflicting index name before the join call and restores it via try/finally

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.94%. Comparing base (edca5a5) to head (577235e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #558      +/-   ##
==========================================
+ Coverage   73.89%   73.94%   +0.05%     
==========================================
  Files          10       10              
  Lines        2777     2783       +6     
  Branches      645      646       +1     
==========================================
+ Hits         2052     2058       +6     
  Misses        451      451              
  Partials      274      274              

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/render.py	82.34% <100.00%> (+0.19%)	⬆️

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