refactor: restrict to only one command per id

[tlambert03]

No description provided.

[codecov]

Codecov Report

Merging #30 (0a01d17) into main (c2dc214) will decrease coverage by 0.28%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
- Coverage   98.94%   98.66%   -0.29%     
==========================================
  Files          30       30              
  Lines        1424     1423       -1     
==========================================
- Hits         1409     1404       -5     
- Misses         15       19       +4     

Impacted Files	Coverage Δ
src/app_model/registries/_commands_reg.py	94.20% <91.66%> (-2.94%)	⬇️
src/app_model/types/_constants.py	96.55% <0.00%> (-3.45%)	⬇️
src/app_model/types/_keybinding_rule.py	96.96% <0.00%> (-3.04%)	⬇️

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