chore(deps): upgrade to AGP 9.3.1 and Gradle 9.5

[BartoszLitwiniuk]

Should be merged after #217

Summary

Upgrades the build toolchain to Android Gradle Plugin 9.3.1 (from 8.11.1) and Gradle 9.5.0 (from 8.14.3), migrating the build scripts to the DSL APIs required by AGP 9.

Changes

Toolchain

• AGP 8.11.1 → 9.3.1 (root build.gradle classpath and settings.gradle plugin declarations)
• Gradle wrapper 8.14.3 → 9.5.0
• Enable org.gradle.tooling.parallel

DSL migration (required by AGP 9)

• Convert android {} block assignments to property syntax (namespace =, minSdk =, versionCode =, …)
• Move compileSdk out of defaultConfig to the android {} block
• Replace removed lintOptions {} with lint {}, and declare targetSdk under lint {} / testOptions {} in the library module (targetSdk is no longer valid in a library's defaultConfig)
• Replace testCoverageEnabled with enableUnitTestCoverage / enableAndroidTestCoverage
• Fix a pre-existing nesting bug in backtrace-library/build.gradle where buildTypes was declared inside itself, so the debug coverage config never applied
• Flatten the redundant nested android {} / defaultConfig {} blocks in example-app/build.gradle

Publishing

• Capture androidGitVersion.name() into libVersion and use it for the Maven coordinates, since android.defaultConfig.versionName is no longer readable at configuration time for library modules

ProGuard

• Switch the example app to proguard-android-optimize.txt to silence a build warning
• Library release build now uses proguard-android-optimize.txt instead of proguard-android.txt