Fix norm behavior, add tests

[Sonja-Stockhaus]

should solve #418 and #372

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.61905% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.20%. Comparing base (478ab27) to head (2cecbf1).

Files with missing lines	Patch %	Lines
src/spatialdata_plot/pl/utils.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #419      +/-   ##
==========================================
+ Coverage   83.83%   85.20%   +1.37%     
==========================================
  Files           8        8              
  Lines        1732     1751      +19     
==========================================
+ Hits         1452     1492      +40     
+ Misses        280      259      -21     

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/render.py	96.89% <100.00%> (+5.73%)	⬆️
src/spatialdata_plot/pl/utils.py	78.27% <94.44%> (+0.26%)	⬆️