Replace ~200ms of real-time sleep() waits with deterministic fake-timer
advances. The dispatcher clamps tickIntervalMs to a 100ms floor, so the
old 30-40ms real sleeps never fired a second interval tick — the
double-dispatch and stop-cancels-timer cases now genuinely exercise a
follow-up tick, making them both faster and stronger.
Fusion-Task-Id: FN-perf
4f9f5e4276