fix: cell density profile

[AhmetNSimsek]

Fixes #276 and #509

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 46 lines in your changes missing coverage. Please review.

Project coverage is 46.14%. Comparing base (d250546) to head (e45a688).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
siibra/features/tabular/cell_density_profile.py	30.30%	46 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #617      +/-   ##
==========================================
+ Coverage   45.99%   46.14%   +0.15%     
==========================================
  Files          75       75              
  Lines        7234     7171      -63     
==========================================
- Hits         3327     3309      -18     
+ Misses       3907     3862      -45     

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[AhmetNSimsek]

Failing tests are due to Allen API so the PR will be merged.