fix: make the close/reset timer tests deterministic

[abelonogov-ld]

closeCancelsPendingTimer and resetCancelsPendingTimer slept for a fraction of the debounce window and then asserted the timer never fired. On a loaded runner that sleep can overshoot the window, and once the timer has begun firing neither close() nor reset() can recall it, so the tests failed for reasons unrelated to the behaviour they cover.

Both now drive a ManualTaskExecutor instead of sleeping, asserting that the scheduled task was cancelled and that draining the queue runs nothing.

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• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

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Overview
Makes closeCancelsPendingTimer and resetCancelsPendingTimer deterministic by driving a ManualTaskExecutor instead of sleeping a fraction of the debounce window.

Those sleeps could overshoot on a loaded runner, so the timer fired before close()/reset() could cancel it. The tests now assert the scheduled task was cancelled and that draining the queue runs nothing.

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