Agent Spec Evaluation Computer improvements

[soufianeamini]

• Use CapacityLimiter over Semaphore
• Limit the amount of concurrent tasks that are running at once (the number of tasks spawned would be at most max_concurrency + 1)
• Producer/worker pattern is not needed anymore as a result

[soufianeamini]

@cesarebernardis The test_unlimited_concurrency test fails if the tasks finish too soon (if I add a bigger delay it succeeds) because it is not required anymore that all tasks start before starting processing. So from testing instead of seeing tasks go up to 200 running tasks concurrently, it ends up hovering around the 60 concurrent tasks range.

Is there a different kind of test you'd want to be implemented or should I just delete it?