feat(ios): Add UIScene life cycle support

[Gibbo97]

feat(ios): Add UIScene lifecycle support

Closes #376.

Apple requires all UIKit apps built with the latest SDK to adopt UIScene lifecycle. In UIScene apps, applicationDidEnterBackground is never called, which prevented background app refresh from being scheduled. This adds the necessary UIScene support per the Flutter plugin migration guide.

Changes:

• SwiftFlutterForegroundTaskPlugin now conforms to FlutterSceneLifeCycleDelegate and registers itself via registrar.addSceneDelegate(instance) so it receives scene lifecycle callbacks
• sceneDidEnterBackground(_:) added to schedule background app refresh in UIScene apps, mirroring what applicationDidEnterBackground does for non-UIScene apps — both coexist for backward compatibility
• FlutterForegroundTaskEarlyRegistration +load added in the Obj-C layer to register the BGTaskScheduler handler at binary load time, before Flutter initialises — required for background launch scenarios where iOS wakes the app to service a refresh task
• isBgTaskRegistered guard added to registerAppRefresh() to prevent a double-registration crash during the UIScene transition period, when host apps may invoke GeneratedPluginRegistrant.register(with:) from both the old and new template locations
• Flutter minimum bumped from >=3.22.0 to >=3.38.0, the version that introduced addSceneDelegate

[Gibbo97]

In addition, after moving to use the new flutter version this library is causing crashes when the app tries to start in the background. Ie when we have scheduled runs with workmanager, or when we try to share content into our app.

These changes resolve all this