spawnIsolateWorker function
Spawn an isolate worker
Implementation
Future<IsolateQueueWorker> spawnIsolateWorker() async {
final commandPort = ReceivePort();
await Isolate.spawn(_isolateWorker, commandPort.sendPort);
// Wait for isolate to send its SendPort
final isolateSendPort = await commandPort.first as SendPort;
commandPort.close();
return IsolateQueueWorker(isolateSendPort);
}