startDiscovery method
Starts a discovery session and returns its session ID.
Implementation
@override
Future<String> startDiscovery(NativeDiscoveryRequest request) async {
startDiscoveryCallCount++;
lastDiscoveryRequest = request;
final sessionId = 'test_session_${DateTime.now().millisecondsSinceEpoch}';
_sessionControllers[sessionId] =
StreamController<NativeDiscoveryEvent>.broadcast();
return sessionId;
}