[Fix] Apply several minor fixes and stability improvements

[felixT2K]

This PR:

• Fix a possible application crash with the auto label annotation
• Fix small polygon shifting after saving and reloading
• Now auto deselect the polygons after tightening
• Add 2 new keybinds for poly drawing and reverting while drawing

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.37%. Comparing base (0d1e0fa) to head (77277fe).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
labeler/views/canvas.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
+ Coverage   80.09%   80.37%   +0.28%     
==========================================
  Files           9        9              
  Lines         839      851      +12     
==========================================
+ Hits          672      684      +12     
  Misses        167      167              

Flag	Coverage Δ
unittests	80.37% <90.90%> (+0.28%)	⬆️

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