Crash when shouldDisplayAboveKeyboardWindow is enabled in non-scene-based apps

[p-x9]

Description

When using TouchTracker in an app that does not adopt the scene-based lifecycle (i.e., uses the traditional UIApplicationDelegate with a single UIWindow instead of UISceneDelegate / UIWindowScene), enabling shouldDisplayAboveKeyboardWindow causes a crash.

Crash Location

The crash occurs in the following method:

keyboardScene(for screen: UIScreen)

Root Cause

In apps without scene-based lifecycle support, there is no UIWindowScene available. The keyboardScene(for:) method appears to assume that a scene-based lifecycle is in use, and likely accesses scene-related APIs that are unavailable or return nil in non-scene-based apps, leading to a crash.

Steps to Reproduce

1. Create an iOS app that uses the traditional AppDelegate-based lifecycle (no UIScene support — no scene delegate, no scene manifest in Info.plist).
2. Add TouchTracker via SPM.
3. Set up TouchTrackingUIView on the app's UIWindow.
4. Enable shouldDisplayAboveKeyboardWindow.
5. Trigger the keyboard (e.g., tap a UITextField).
6. → Crash in keyboardScene(for:).

Expected Behavior

TouchTracker should gracefully handle the case where the app does not use a scene-based lifecycle. If the keyboard window scene is not available, it should fall back to a safe default (e.g., skip the above-keyboard display or use the app's main window instead).