Whether the subscription would need to buffer events.
This is the case if the controller's stream has a listener and it is paused, or if it has not received a listener yet. In that case, the controller is considered paused as well.
A broadcast stream controller is never considered paused. It always forwards its events to all uncanceled subscriptions, if any, and let the subscriptions handle their own pausing and buffering.
bool get isPaused;