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

❌ Patch coverage is 51.78571% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.95%. Comparing base (70da5b9) to head (9313a40).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/spatialdata_plot/pl/render.py	38.88%	22 Missing ⚠️
src/spatialdata_plot/pl/utils.py	75.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #471      +/-   ##
==========================================
- Coverage   85.11%   83.95%   -1.16%     
==========================================
  Files           8        8              
  Lines        1807     1839      +32     
==========================================
+ Hits         1538     1544       +6     
- Misses        269      295      +26     

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/utils.py	78.14% <75.00%> (-0.22%)	⬇️
src/spatialdata_plot/pl/render.py	91.52% <38.88%> (-4.98%)	⬇️

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[Sonja-Stockhaus]

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