Add more typing, separate tests and prepare package for release

[goanpeca]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 62.06897% with 33 lines in your changes missing coverage. Please review.

Project coverage is 44.76%. Comparing base (82d8702) to head (8515b73).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
napari_update_checker/qt_update_checker.py	0.00%	18 Missing ⚠️
napari_update_checker/utils.py	56.66%	13 Missing ⚠️
napari_update_checker/_tests/test_utils.py	94.87%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #3       +/-   ##
===========================================
+ Coverage   19.31%   44.76%   +25.45%     
===========================================
  Files           3        3               
  Lines         145      172       +27     
===========================================
+ Hits           28       77       +49     
+ Misses        117       95       -22     

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