Fixes #9: cancel feature

[valorwing]

Introduce a cancel feature to the debounce utility, allowing immediate flush
of pending actions during graceful shutdown. Ensures the latest state is saved
without waiting for the original debounce delay.

This improves reliability when shutting down applications that use
debounced writes, preventing potential data loss.

Fixes #9

[bep]

Thanks for this, looks good. A little practical tip for the future: GitHub puts the Git commit message into a newly created PR's description field, but it doesn't go the other way around. So my workflow here is to write the text I want to show up in the Git history when I'm committing to Git.

[valorwing]

Thanks for the advice. Glad I could contribute.