As firstPost doesn't work on Android 34+ devices

- Add support for ApplicationStartInfo API on Android 15+ (API 35) for more accurate cold/warm start detection
- Add null safety check for ActivityManager service
- Fix detection logic to prevent legacy methods from running when API 35+ already determined start type
- Set app start type to WARM when app moves to background (process stays alive)
- Add comprehensive test coverage with notification-triggered start scenarios

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

…entry-java into fix/app-start-warm-detection

Add custom SentryShadowActivityManager to mock ApplicationStartInfo
for testing cold/warm start detection on Android 15 (API 35).

Tests verify the new getHistoricalProcessStartReasons() code path
and fallback behavior when the list is empty or invalid.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>