Idle CU sweep cannot reclaim a computing unit whose execution is stuck in a non-terminal state

[yrenat]

Feature Summary

Follow-up to #6046.

Problem

The idle Kubernetes computing unit sweep treats a computing unit as busy whenever any of its
workflow_executions rows carries a non-terminal status code (status NOT IN (3, 4, 5)). That
test has no time bound, so an execution row left stuck in a non-terminal state keeps its computing unit off the sweep indefinitely, even though the unit is doing no work.

But the problem is, nothing else reclaims it either: ComputingUnitHelpers.reconcileVanishedKubernetesUnits only
runs when someone calls a listing endpoint, and it only checks whether the pod is already gone,
not whether the execution row is stuck somewhere. A live pod with a stuck row is missed on both paths.

maptoStatusCode also maps UNKNOWN (and TERMINATED) to -1, which is not in {3,4,5}. A row whose final status is -1 pins its unit off the sweep permanently. Fixing that means changing the codes amber writes, not this sweep's predicate.

Proposed Solution or Design

• Ignore a non-terminal execution row whose last_update_time is older than its own timeout.
• Check execution status codes against actual pod state on a schedule, rather than only on a
  listing request.

Either is a larger change than #6046 should carry, hence this follow-up.

Affected Area

No response