Unref WebSocket stop timeout to prevent lingering timers

[BelfordZ]

Summary

• avoid keeping event loop alive by calling unref on WebSocketServerTransport stop timeout
• add unit test to ensure timeout is unrefed

Testing

• npm test

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https://chatgpt.com/codex/tasks/task_e_68b33c68613c832faf956dcd076a4927

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.96%. Comparing base (eee4a4d) to head (75f9500).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #866   +/-   ##
=======================================
  Coverage   98.96%   98.96%           
=======================================
  Files           9        9           
  Lines         289      290    +1     
  Branches       43       43           
=======================================
+ Hits          286      287    +1     
  Misses          3        3           

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