[desktop_webview_window] Webview doesn't work on macOS

When I try to launch a webview window, it instead launches a copy of the main app, and when that tries to launch a webview window, it crashes.

Reproduce Steps

lib/main.dart:

import 'package:flutter/material.dart';
import 'package:desktop_webview_window/desktop_webview_window.dart';

void main(List<String> arguments) {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: OutlinedButton(
          child: FlutterLogo(),
          onPressed: () {
            WebviewWindow.create().then((webview) {
              webview.launch('example.com');
            });
          },
        ),
      ),
    ),
  );
}

Run the app, press the button. Then, press the button on the new window that launched.

what it looks like

Version (please complete the following information):

• Flutter Version: 3.22.0-31.0.pre.3
• OS: macOS 14.4.1
• plugin: desktop_webview_window

Start by reproducing the issue on macOS 14.4.1 using the lib/main.dart example and the stated Flutter version. Then inspect the desktop_webview_window macOS launch path; done means WebviewWindow.create() opens the requested webview instead of another copy of the main app or a crashing window.