Update Android toolchain to AGP 9.2.0 / Gradle 9.5.1 / Kotlin 2.3.21

[n13]

Summary

Upgrades the Android build to the latest stable toolchain versions and fixes the Gradle 9 incompatibility in the Cargokit Rust integration.

Upgraded versions

Tool	Before	After
Gradle	8.13	9.5.1
Android Gradle Plugin	8.13.2	9.2.0
Kotlin Gradle Plugin	2.2.0	2.3.21
Google Services plugin	4.3.15	4.4.4

Fixes

• Cargokit Gradle 9 compatibility (quantus_sdk/rust_builder/cargokit/gradle/plugin.gradle): Gradle 9 removed Project.exec, which the Cargokit plugin relied on, causing builds to fail with Could not find method exec() for arguments [...] on project ':rust_lib_quantus_wallet'. Migrated CargoKitBuildTask to use the injected ExecOperations service (the official replacement per Gradle 9 upgrade guide).
• Google Services plugin bump to 4.4.4: required for AGP 9.x compatibility (older versions referenced the now-removed applicationVariants API).
• gradle.properties tweaks: added several android.* flags surfaced by the AGP migrator.

Known follow-ups (not in this PR)

• Built-in Kotlin migration is deferred: Flutter 3.44's own Gradle plugin doesn't yet support android.newDsl=true, and many third-party Flutter plugins (flutter_timezone, local_auth_android, mobile_scanner, play_install_referrer, share_plus, shared_preferences_android, telemetrydecksdk, app_links, ...) still apply the legacy kotlin-android plugin. The Flutter team explicitly recommends keeping builtInKotlin=false and newDsl=false until those migrate. The "future Flutter" warnings during build are informational and not fatal.

Test plan

• flutter build apk succeeds (verified: Built build/app/outputs/flutter-apk/app-release.apk (94.3MB) in ~93s)
• Smoke-test the release APK on a physical Android device
• Verify the Rust bridge (rust_lib_quantus_wallet) still works at runtime (key signing, wormhole, etc.)
• Confirm Firebase / FCM still wires up correctly with google-services 4.4.4

Notes

We get the following warnings on flutter builds - but "fixing" them causes actual build errors, so this is just flutter being a little bit retarded...

WARNING: Your Android app project: app located at: /Users/elohim/play/quantus-network/quantus-apps/mobile-app/android/app/build.gradle
applies the Kotlin Gradle Plugin, which will cause build failures in future versions of Flutter. 
Please migrate your app to Built-in Kotlin using this guide: https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin/for-app-developers

WARNING: Your app uses the following plugins that apply Kotlin Gradle Plugin (KGP): flutter_timezone, local_auth_android, mobile_scanner, play_install_referrer, share_plus, shared_preferences_android, telemetrydecksdk
Future versions of Flutter will fail to build if your app uses plugins that apply KGP.

Please check the changelogs of these plugins and upgrade to a version that supports Built-in Kotlin.
If no such version exists, report the issue to the plugin. If necessary, here is a guide on filing 
an issue against a plugin: https://docs.flutter.dev/release/breaking-changes/migrate-to-built-in-kotlin/for-app-developers#report-incompatible-kotlin-gradle-plugin-usage-to-plugin-authors

[dewabisma]

GTG!

That warning is concerning though.

[n13]

GTG!

That warning is concerning though.

Tried to fix it which then broke the build ... we can fix this once flutter actually doesn't allow this anymore by that time hopefully they've also fixed the kinks and all the packages have been updated