Fixes #298: Repeatedly appending parent path to flatFiles

[mayank-singh-sikarwar]

Purpose: Fix for appending parent path to CSV file paths in cosmx.py reader module.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.48%. Comparing base (fe474c6) to head (cb147e2).
⚠️ Report is 49 commits behind head on main.

Files with missing lines	Patch %	Lines
src/spatialdata_io/readers/cosmx.py	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #305      +/-   ##
==========================================
- Coverage   49.53%   49.48%   -0.06%     
==========================================
  Files          26       26              
  Lines        2709     2712       +3     
==========================================
  Hits         1342     1342              
- Misses       1367     1370       +3     

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/cosmx.py	18.51% <0.00%> (-0.43%)	⬇️

... and 3 files with indirect coverage changes

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