close method
Closes the web socket connection.
Implementation
Future<void> close() async {
await _channel.invokeMethod(_METHOD_CHANNEL_DISCONNECT);
// message stream
_eventsMessage = null;
await _onMessageSubscription?.cancel();
_onMessageSubscription = null;
_eventsClose = null;
await _onCloseSubscription?.cancel();
_onCloseSubscription = null;
}