🧪 test: add unit tests for CoalescedTimeout class

[MarsLuay]

🧪 What: Added unit test suite for CoalescedTimeout class in tests/coalesced-timeout.test.mjs.

📊 Coverage: Tests cover:

• Scheduling and delayed task execution.
• Coalescing duplicate schedule calls when a timer is already pending.
• Resetting timeout state upon execution to allow subsequent scheduling.
• Canceling active timeouts to prevent task execution.
• Safe no-op behavior when cancel() is called with no active timeout.
• Rescheduling after cancellation.

✨ Result: Improved test coverage and reliability for timer coalescing logic.

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PR created automatically by Jules for task 13995564058853243034 started by @MarsLuay

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