sendDatagram function
Sends bytes as a single UDP datagram to address:port.
Returns immediately; the socket's write callback reports completion
via its JSFunction argument, which callers may ignore for fire-and-
forget semantics.
Implementation
void sendDatagram(
DgramSocket socket,
Uint8List bytes,
String address,
int port,
) {
socket.send(bytes.toJS, port.toJS, address.toJS);
}