Replace the real ScheduledExecutorService backing ReplyPushLoop in this one
test with ManualScheduler, a fake that only runs a tick when the test calls
runDueTasks(). The old test bet a 300ms backoff was wide enough that
collecting the ticket always won the race against the scheduler's own timer
- true on an idle machine, false under a loaded full-suite run, which is
exactly the flake reported.
The rewritten test also waits on setAfterFinishAsyncTaskCompleteHookForTest
(already used elsewhere in this file) instead of polling Phase.DONE, so it
does not race CompletableFuture.complete()'s own publish-then-run-dependents
gap (fleetd #399) while proving ReplyPushLoop.onTicketTerminal really ran
before the ticket is collected.
Verified: backoff=1 (the most hostile value) still passes; mutating
ReplyPushLoop.ticketCollected to a no-op turns the test red with the same
assertion message the original flake reported; three consecutive full-suite
runs are green (1841/1841 each).
Dai Ha