nan handling for continuous and categorical coloring

[Sonja-Stockhaus]

Fix coloring of shapes, labels and points when there are nan values in the vectors to color by

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.51%. Comparing base (27878f1) to head (2c02cee).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #427      +/-   ##
==========================================
+ Coverage   85.21%   85.51%   +0.29%     
==========================================
  Files           8        8              
  Lines        1759     1795      +36     
==========================================
+ Hits         1499     1535      +36     
  Misses        260      260              

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/render.py	97.14% <100.00%> (+0.24%)	⬆️
src/spatialdata_plot/pl/utils.py	78.40% <100.00%> (+0.06%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.