fix(android): make onConfigurationChanged param non-nullable (#1472)

## Description

Android's `View.onConfigurationChanged(@NonNull Configuration
newConfig)` is now strictly enforced as non-null by Kotlin under the
compileSdk shipped with React Native 0.86. The overrides in
`EdgeToEdgeReactViewGroup` and `KeyboardBackgroundViewGroup` declared
the parameter as `Configuration?`, which no longer matches the parent
signature and breaks the build:

```
e: EdgeToEdgeReactViewGroup.kt:97 'onConfigurationChanged' overrides nothing.
Potential signatures for overriding:
fun onConfigurationChanged(newConfig: Configuration): Unit
e: KeyboardBackgroundViewGroup.kt:20 'onConfigurationChanged' overrides nothing.
e: KeyboardBackgroundViewGroup.kt:21 Argument type mismatch: actual type
is 'Configuration?', but 'Configuration' was expected.
```


Dropping the `?` matches the parent signature. The change is
backwards-compatible with older React Native / compileSdk versions
because the parent method is exposed there as a Kotlin platform type
(`Configuration!`), which accepts a non-nullable override.

## 💡 Motivation and Context

- react-native 0.86 support

## 📢 Changelog

### Android

- Make `onConfigurationChanged` param non-nullable

## 🤔 How Has This Been Tested?

- Android build (`./gradlew
:react-native-keyboard-controller:compileReleaseKotlin`) succeeds
against React Native 0.86
- Android build still succeeds against the previously supported React
Native versions
- Theme change still triggers `setBackgroundColor` /
`reApplyWindowInsets` at runtime

## 📸 Screenshots (if appropriate):

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## 📝 Checklist

- [ ] CI successfully passed
- [ ] I added new mocks and corresponding unit-tests if library API was
changed