resetReplayOnRegisterStateForTest method
Resets the replay-on-register gate fields so idempotency/replay unit tests
are order-independent (module-level statics persist across cases in one VM;
see Issue 63). Call from the relevant tests' setUp().
Implementation
@visibleForTesting
void resetReplayOnRegisterStateForTest() {
_hasAuthStateChangeListenerRunAtLeastOnce = false;
_lastDeliveredAuthUid = null;
}