A new MaxResultsPerPermit option is introduced to cap how many index
results an index worker can process at a time. If the max is exceeded, the
index worker must yield the permit back and acquire it again
(potentially waiting) to continue processing the results.

This cap ensures large queries don't dominate the finite number of index
workers allowed to run concurrently and lock out smaller queries. The
idea is users would want to set the max large enough so the vast
majority of typical queries can finish with only a single permit
acquisition.

…l-worker-pool-iter

…l-worker-pool-iter