Update templates and tests to use UIScene life cycle

[rolfbjarne]

"In the next major release following iOS 26, UIScene life cycle will be required when building with the latest SDK.": https://developer.apple.com/videos/play/wwdc2025/282/?time=143

This means we'll have to update our stuff to use the UIScene life cycle:

• templates
• test suites

References:

• https://developer.apple.com/videos/play/wwdc2025/282/
• https://developer.apple.com/documentation/technotes/tn3187-migrating-to-the-uikit-scene-based-life-cycle