Calculate label mask within napari-tomotwin

[thorstenwagner]

Calculating it here makes it easier for the user. They simply don't need to provide it.

[thorstenwagner]

This PR is also setting the label of the progress bar and refactoring the the load_umap tools.

[codecov]

Codecov Report

Attention: 134 lines in your changes are missing coverage. Please review.

Comparison is base (6dcbd4a) 33.77% compared to head (5043802) 26.17%.
Report is 13 commits behind head on main.

Files	Patch %	Lines
src/napari_tomotwin/load_umap.py	0.00%	121 Missing ⚠️
src/napari_tomotwin/make_targets.py	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
- Coverage   33.77%   26.17%   -7.61%     
==========================================
  Files           5        5              
  Lines         225      298      +73     
==========================================
+ Hits           76       78       +2     
- Misses        149      220      +71     

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