unary method
Implementation
Future<GenericMessage> unary(String service, String method,
GenericMessage req,
{Map<String, String>? metadata, Duration? timeout}) async {
final m = _method(service, method);
final resp = _BoundMessage(m.output!, GenericMessage(m.output), _model);
await _channel.unary(m.path, _BoundMessage(m.input!, req, _model), resp,
metadata: metadata, timeout: timeout);
return resp.generic;
}