Store coordinates as unscaled pixel coordinates + scaling factor when exporting to geff

[AnniekStok]

Scale world coordinates to pixel coordinates when exporting to geff, and scale back at import to align with the geff spec, as a potential solution for #261

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.68%. Comparing base (b63ba93) to head (c265f85).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/funtracks/import_export/geff/_import.py	85.18%	4 Missing ⚠️
src/funtracks/import_export/geff/_export.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #262      +/-   ##
==========================================
- Coverage   93.78%   93.68%   -0.10%     
==========================================
  Files          59       59              
  Lines        3284     3328      +44     
==========================================
+ Hits         3080     3118      +38     
- Misses        204      210       +6     

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[cmalinmayor]

Design decision: segmentation shape and voxel size should be stored in tracksdata for in-graph segmentations, and thus saved in the geff. External segmentations should have the same metadata in their appropriate file format standards.

Aciton item for now: Always show the scale widget pre-filled with whatever metadata is present, and let the user change it during import if needed. Might need a slight hack for our internal save/load to ignore the scale for now.

Ideally, later: we should save in world coordiantes (no axis scales), and save the segmentation metadata in tracksdata (blocked by this not existing in tracksdata for voxel size yet).