send method
Queues data for transmission. Must return immediately without blocking;
the platform drains the queue off the calling isolate.
The queue is unbounded and lossless: every byte accepted here is either eventually handed to the OS or reported lost via flush / the terminal disconnect — a transport must never silently drop accepted bytes.
Implementation
@override
void send(Uint8List data) {
if (_closed) throw const BluetoothWriteException('transport closed');
sent.add(data);
_pendingWriteBytes += data.length;
}