Check possible memory leaks

[gabrielbmoro]

In jujuba_widget.dart, we define the main entry point of the library. There are two areas that should be reviewed for potential memory leaks:

• Stream listener

widget.commander.stream.listen(
    (jsCommand) => _runJavascript(jsCommand),
);

• WebViewController instance (_controller)

Both should be carefully managed to ensure they are properly disposed of when no longer needed.