fix image rendering (clipping warning)

[Sonja-Stockhaus]

As discussed @timtreis, part of the code from #451 to do a first smaller pull request without the PCA approach

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 49.05660% with 27 lines in your changes missing coverage. Please review.

Project coverage is 83.88%. Comparing base (c5cb734) to head (2f410d8).

Files with missing lines	Patch %	Lines
src/spatialdata_plot/pl/render.py	38.88%	22 Missing ⚠️
src/spatialdata_plot/pl/utils.py	70.58%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #471      +/-   ##
==========================================
- Coverage   85.00%   83.88%   -1.12%     
==========================================
  Files           8        8              
  Lines        1794     1831      +37     
==========================================
+ Hits         1525     1536      +11     
- Misses        269      295      +26     

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/utils.py	78.08% <70.58%> (-0.11%)	⬇️
src/spatialdata_plot/pl/render.py	91.44% <38.88%> (-5.03%)	⬇️

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[Sonja-Stockhaus]

Additional tests and the PCA aggregation for > 3 channels are in #451