Add PID control feedback to adaptive scheduler queue

The current scheduler's adaptive queue size has no hysteresis and is probably more easily attacked as a result.

Details

Adaptive queue size is needed to avoid DOS transactions that makes long queues of deferred transactions that must be re-scanned over and over again. We need to evaluate using a little more control theory to ensure that we do not overreact to queue size changes, nor react too slowly.

Acceptance Criteria

• Simulator-based evaluation shows that the queue-size adjustment keep scheduler execution times low. (This needs to be improved to be more objective.)