Abstract out concurrency limiter's queues

Extracted from !6353 (closed)

This MR adds two changes:

• Replace the concurrency limiter's ticker generator with context timeout. The ticker generator returns a new ticker when called to handle the timeout event. Replace it with a context timeout is more elegant. A prerequisite is to implement a test helper that allows the test trigger the timeout event manually.
• Abstract out concurrency limiter's queues. The concurrency limiter controls the concurrency and queueing mechanism using two buffered channels. Naturally, we can consider them as two weighted semaphores. This commit extracts the core operations of those two semaphores to a staticSemaphore struct. This extraction also standardizes the interface so that the forward commits can swap in another semaphore implementation (demonstrated in !6353 (closed)).

Manual tests

I performed some manual tests on the local to verify the refactoring still works as expected.

	Concurrency limit	Pack-object limit
Under the limit	✅	✅
Wait in queue	✅	✅
Wait when max_queue_size = 0	✅	✅
Exceed queue size	✅	✅
Timeout waiting in queue	✅	✅
Timeout when max_queue_size = 0	✅	✅