Enhanced numerical obs mapping support and method consistency

[Marius1311]

Method renaming and numerical obs mapping improvements

Closes #29

Summary

Renamed 4 methods for consistency and improved numerical observation mapping behavior.

Changes

• Renamed transfer_labels → map_obs
• Renamed transfer_expression → map_layers
• Renamed transfer_embeddings → map_obsm

[codecov]

Codecov Report

❌ Patch coverage is 84.48276% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.30%. Comparing base (7edb7fe) to head (6071e84).
⚠️ Report is 127 commits behind head on main.

Files with missing lines	Patch %	Lines
src/cellmapper/model/cellmapper.py	85.96%	8 Missing ⚠️
src/cellmapper/model/evaluate.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
- Coverage   85.67%   85.30%   -0.38%     
==========================================
  Files           9        9              
  Lines         747      762      +15     
==========================================
+ Hits          640      650      +10     
- Misses        107      112       +5     

Files with missing lines	Coverage Δ
src/cellmapper/model/evaluate.py	80.00% <0.00%> (ø)
src/cellmapper/model/cellmapper.py	85.78% <85.96%> (-1.64%)	⬇️

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