fix: AGP 8+ namespace compatibility and dependency updates

Summary

This PR fixes build failures when using ar_flutter_plugin with Android Gradle Plugin 8.0+ and newer Flutter/Dart versions.

Problem

Starting with AGP 8.0, the namespace property is required in build.gradle. The plugin was failing to build with: Namespace not specified. Specify a namespace in the module's build file.

Additionally, there were compatibility issues with:

• Kotlin version too old for newer AGP
• JVM target mismatch between Java and Kotlin compilation
• permission_handler using deprecated v1 Flutter embedding
• Gradle wrapper in example app incompatible with Java 21

Changes

android/build.gradle

• Added namespace 'io.carius.lars.ar_flutter_plugin'
• Updated Kotlin version: 1.3.50 → 1.8.0
• Updated Android Gradle Plugin: 4.1.0 → 7.3.0
• Added kotlinOptions { jvmTarget = '1.8' }

android/src/main/AndroidManifest.xml

• Removed redundant package attribute (now defined via namespace)

pubspec.yaml

• Updated permission_handler: ^10.4.5 → ^12.0.0

example/android/gradle/wrapper/gradle-wrapper.properties

• Updated Gradle: 7.5 → 8.5

Testing

• Tested with Flutter 3.x stable
• Tested with AGP 8.1.0
• Verified AR functionality on Android device

Checklist

• No breaking changes
• Tested on Android
• [x ] Tested on iOS (N/A for these changes)