chore: prepare release v6.2.2

[TheRealAgentK]

Summary

• bump the provider version to 6.2.2 and version code to 60202099
• document the September CI, sample-app, build-tool, and dependency maintenance
• update the README's stale stable-release reference from 6.0.0 to 6.2.2

Release rationale

This is a patch release. It contains no provider source or public API changes. The consumer-visible change is the provider's AppCompat runtime dependency update from 1.7.1 to 1.8.0; minimum Android SDK remains API 23 and AAR minCompileSdk remains 36.

Validation

• ./gradlew --no-daemon spotlessCheck app:lint provider:lint app:assembleDebug provider:assembleDebug provider:test :provider:publishToMavenLocal
• ./gradlew --no-daemon connectedCheck on an Android 6.0 / API 23 emulator (4 tests passed)
• inspected locally published com.raygun:raygun4android:6.2.2 POM: expected coordinates and AppCompat 1.8.0 runtime dependency
• inspected release AAR metadata: minCompileSdk=36
• inspected release BuildConfig: VERSION_NAME=6.2.2, VERSION_CODE=60202099