onNotify is a stream of BLE notifications.
To add a new notification listener, use startNotify method.
This stream will emit the raw bytes of the notification.
setMtu sets the MTU size for the BLE connection.
The MTU size is the maximum number of bytes that can be sent in a single packet, also, MTU means
Maximum Transmission Unit and it is the maximum size of a packet that can be sent in a single transmission.
startNotify starts listening to notifications from a BLE characteristic.
To stop listening, use stopNotify method and to get the notifications, use onNotify stream.