Using WebviewScaffold to load URLs doesn't work in iOS

## System info

Issue occurs on: iOS
Plugin version: 0.4.0
Flutter doctor output:

```
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.16.2, on macOS 14.1.2 23B92 darwin-arm64, locale en-IN)
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 15.0.1)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.1)
[✓] Connected device (2 available)
[✓] Network resources

• No issues found!
```

## Steps to Reproduce

1. I am using the WebViewScaffold to launch a URL. This approach works fine on Android and the page is loaded. However, on iOS, it gives a white blank screen.
2. Followed all the steps mentioned in the documentation and the key "NSAppTransportSecurity" is added to the Info.plist file as recommended in the documentation.
3. The iOS app launches the URL and works fine if we use an instance of the FlutterWebViewPlugin to call the "launch()" method instead of the WebViewScaffold implementation.
4. There are no errors logged on the console while running it.
5. Here is the code that renders the view inside a StatefulWidget

```
...
return SafeArea(
child: WebviewScaffold(
url: _url,
mediaPlaybackRequiresUserGesture: false,
useWideViewPort: true,
appCacheEnabled: true,
geolocationEnabled: true,
invalidUrlRegex:
r'^(https:\/\/api\.whatsapp\.com|https:\/\/apps\.apple\.com|https:\/\/play\.google\.com|tel:|mailto:|https:\/\/www\.facebook\.com|https:\/\/www\.youtube\.com|https:\/\/www\.instagram\.com)',
debuggingEnabled: true,
),
);
```

## Logs

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```

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```

Commencez par reproduire le comportement d’iOS via le point d’entrée WebviewScaffold, en le comparant à FlutterWebViewPlugin.launch() et en examinant la configuration documentée de Info.plist NSAppTransportSecurity. L’issue ne nomme aucun fichier source ni aucun test ; commencez donc par localiser l’implémentation WebView pour iOS et établir une URL ainsi qu’un cas d’échec reproductibles ; le travail est considéré comme terminé lorsque l’URL s’affiche via WebviewScaffold sur iOS sans régression du comportement sur Android.

Rédigé par le modèle d'indexation à partir du texte de l'issue.