Implement presence scores and allow evaluation per group

[Marius1311]

Includes a groupby parameter for both presence scores and expression transfer evaluation.

closes #13

[codecov]

Codecov Report

Attention: Patch coverage is 96.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.40%. Comparing base (6c461b6) to head (9b8c544).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cellmapper/evaluate.py	96.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
+ Coverage   84.23%   85.40%   +1.17%     
==========================================
  Files           6        6              
  Lines         425      466      +41     
==========================================
+ Hits          358      398      +40     
- Misses         67       68       +1     

Files with missing lines	Coverage Δ
src/cellmapper/evaluate.py	87.85% <96.42%> (+4.01%)	⬆️

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