Improve the decompression of star coloring for AbstractMatrix

[amontoison]

Use compressed_indices from the StarColoringResult.

[gdalle]

really good idea!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (a7a4c37) to head (bb4b579).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #209   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines         1647      1638    -9     
=========================================
- Hits          1647      1638    -9     

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