Support AGP 9 built-in Kotlin

[nohli]

Fixes #119

[Copilot]

Pull request overview

This PR updates the plugin’s Android build configuration to be compatible with Android Gradle Plugin (AGP) 9+ and Flutter’s “built-in Kotlin” mode, addressing #119 by avoiding plugin-owned AGP/Kotlin classpaths and only applying the Kotlin Gradle plugin when needed.

Changes:

• Remove plugin-owned buildscript classpaths for AGP/Kotlin and conditionally apply kotlin-android based on AGP major version and android.builtInKotlin.
• Migrate JVM target configuration from kotlinOptions to the newer kotlin { compilerOptions { ... } } DSL (plugin + example app).
• Update example project tooling to AGP 9.1.1 / newer Gradle wrapper, and bump package version + changelog/docs.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
android/build.gradle	Removes plugin-owned AGP/Kotlin classpaths; conditionally applies Kotlin plugin and updates Kotlin compiler/JVM target config for AGP 9 compatibility.
example/android/app/build.gradle	Removes explicit Kotlin Android plugin application and configures Kotlin JVM target via kotlin { compilerOptions }.
example/android/settings.gradle	Updates example to AGP 9.1.1 and removes explicit Kotlin plugin management entry.
example/android/gradle/wrapper/gradle-wrapper.properties	Updates Gradle wrapper version used by the example Android project.
example/android/gradle.properties	Adds android.newDsl=false to example project properties.
pubspec.yaml	Bumps package version to 0.5.2.
example/pubspec.lock	Updates resolved dependency versions / SDK metadata for the example app.
README.md	Documents AGP 9 / built-in Kotlin compatibility and the rationale for the build changes.
CHANGELOG.md	Adds 0.5.2 release notes describing the AGP 9 / Kotlin compatibility work.

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated no new comments.