Fix overlapping audio notifications for high-priority messages

[LaurenceJJones]

fix #850

• Add audioNotification utility to manage single Audio instance reuse
• Debounce audio playback with 300ms cooldown after playback ends
• Skip playback if audio is currently playing or in cooldown window
• Replace per-message Audio creation with shared instance in reactions.ts

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.14%. Comparing base (71e38b9) to head (2ab9fb5).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #869   +/-   ##
=======================================
  Coverage   79.14%   79.14%           
=======================================
  Files          56       56           
  Lines        2225     2225           
=======================================
  Hits         1761     1761           
  Misses        360      360           
  Partials      104      104           

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[jmattheis]

Thanks for the contribution. I've added a review for explanation, but will fix the remarks in an own commit. You don't have to do anything.