feat: add clear_queued function to discard queued callbacks

[tlambert03]

closes #436

[codspeed]

Merging this PR will not alter performance

✅ 67 untouched benchmarks

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_{Comparing tlambert03:clear-queue (276e8a8) with main (7b28c2a)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.76%. Comparing base (7b28c2a) to head (276e8a8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #441   +/-   ##
=======================================
  Coverage   99.76%   99.76%           
=======================================
  Files          23       23           
  Lines        2548     2559   +11     
=======================================
+ Hits         2542     2553   +11     
  Misses          6        6           

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