if the connection times out, then the promise is rejected and the connection state set to `not-connected`.
If the connect still succeeds, the incoming package will handle the `CONNECT` frame and the client will emit an error, see https://github.com/romainneutron/stomp/blob/a70640767f290d55aecca79e03fd24f5f91762ce/src/React/Stomp/Client/IncomingPackageProcessor.php#L46