connectionLost property Null safety
Occurs when the SDK cannot reconnect to Agora's edge server 10 seconds after its connection to the server is interrupted.
The SDK also triggers this callback when it cannot connect to the server 10 seconds after calling RtcChannel.joinChannel, regardless of whether it is in the channel or not.
If the SDK fails to rejoin the channel 20 minutes after being disconnected from Agora's edge server, the SDK stops rejoining the channel.
EmptyCallback typedef does not include any parameter.