feat: add toggled to command

[tlambert03]

Adds the ability to toggle menu item based on a condition

[codecov]

Codecov Report

Merging #41 (56ec175) into main (b3f1a10) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #41   +/-   ##
=======================================
  Coverage   97.53%   97.53%           
=======================================
  Files          31       31           
  Lines        1621     1625    +4     
=======================================
+ Hits         1581     1585    +4     
  Misses         40       40           

Impacted Files	Coverage Δ
src/app_model/backends/qt/_qaction.py	96.87% <100.00%> (+0.15%)	⬆️
src/app_model/types/_command_rule.py	100.00% <100.00%> (ø)

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