SubscriptionRef when no longer needed. I’m concerned that if any listeners of SubscriptionRef.changes(ref) forget to stop listening, the SubscriptionRef might never be garbage collected, since active listeners would keep it in memory.ref.pubsub seems wrong, since it feels like manually shutting down part of the implementation of SubscriptionRef.SubscriptionRef expose a shutdown method directly?SubscriptionRef guide doesn't even mention anything about cleaning up resources.