* perf(engine): requeue rate limited items without a transaction

Every queue loop tick wrapped RequeueRateLimitedQueueItems in BEGIN /
statement / COMMIT even though it almost always moves no rows, holding a
pooled connection for three round trips per queue per tick. Under high
queue fan-out that hold time saturates the scheduler's pool and the wait
shows up as queue latency. The statement is a single atomic CTE, so run it
in autocommit and only upsert the queue when rows were actually moved.

* fix: keep the per-queue last_active keepalive in RequeueRateLimitedItems

Skipping upsertQueues when no rows moved dropped the only thing keeping a
queue active while its pending work sits in v1_rate_limited_queue_items for
more than a day; the queue would fall out of ListQueues, lose its queuer,
and never be requeued. Run the (cache-gated) upsert every call as before,
still outside a transaction.