unsubscribe method
Implementation
void unsubscribe(String subscriberId, {int? waitUntilMessageCount}) {
if (this._protocolHandler == null)
throw new Exception("Client not connected yet, operation not allowed");
try {
_protocolHandler!.unsubscribe(
subscriberId,
waitUntilMessageCount: waitUntilMessageCount,
);
_subscriptions.removeWhere(
(subscription) => subscription.subscriptionId == subscriberId);
} catch (err) {}
}