faster regionprops annotator

[TeunHuijben]

In the majority of cases where the RegionpropsAnnotator is called, it is only to retrieve the position key (mainly in SolutionTracks.init, where the pos key is recomputed). It is overkill to use regionprops for this on every single mask.

This PR implements a faster method to find the position from mask+bbox without having to go through the expensive regionprops.

This path is not part of the current benchmark, but in my hands, it's >3x faster.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.72%. Comparing base (6baed08) to head (1b213ca).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #257      +/-   ##
==========================================
- Coverage   93.78%   93.72%   -0.07%     
==========================================
  Files          59       59              
  Lines        3284     3297      +13     
==========================================
+ Hits         3080     3090      +10     
- Misses        204      207       +3     

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