add extract package cmd in warning for simple fix

[StRigaud]

integrate the optional extra package for linux and macos into a warning message:

MacOS users may need to install the following package: mamba install -c conda-forge ocl_icd_wrapper_apple 
Linux users may need to install the following package: mamba install -c conda-forge ocl-icd-system

if no backend founds when importing pyclesperanto package

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.55%. Comparing base (734faf4) to head (60856e5).

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #223   +/-   ##
=======================================
  Coverage   86.55%   86.55%           
=======================================
  Files          18       18           
  Lines        1607     1607           
=======================================
  Hits         1391     1391           
  Misses        216      216           

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