Isolate the blocking-queue futexes on their own cache lines

[vadimskipin]

FiberBlockingQueue laid spaceAvailable and itemAvailable on the line holding BoundedQueue's dequeuePos, so every producer's itemAvailable post invalidated the consumer's dequeue cursor and every dequeue invalidated the line producers read and post at enqueue. Aligning each futex to its own line measured +14% on a 100-producer, one-consumer enqueue-heavy workload.

[praktika-gh]

Workflow [PR], commit [2312fcb]

Summary: ⏳

job_name	test_name	status	info	comment
Test ARM (release)		FAIL
	Bench	FAIL

[Copilot]

Pull request overview

This PR improves FiberBlockingQueue throughput under high producer contention by reducing false sharing: the spaceAvailable and itemAvailable futexes are moved onto separate cache lines so producer/consumer signaling doesn’t constantly invalidate the queue cursor cache lines.

Changes:

• Cache-line align spaceAvailable futex to reduce interference with the consumer-side dequeue cursor.
• Cache-line align itemAvailable futex so producer posts don’t invalidate consumer hot data.
• Add inline documentation explaining the intended cache-line ownership pattern.

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