perf(run-engine): bound and meter the concurrency-set reconcile in the dequeue scripts

The run queue's self-heal for saturated concurrency sets is now bounded
and configurable (page size, lock TTL, passes per dequeue, on/off) and
reports its work through OpenTelemetry metrics and span attributes.
Defaults preserve existing behaviour apart from capping passes per
dequeue script at 2.

Mono-RevId: fa05bcd6515f5905f3be52abeebaeeeeb0287617