Batch 9: Integration and unit tests

[JusterZhu]

Batch 9: Tests

Tasks

1. DownloadPlanBuilder tests — Cross-version selection, version chain, frozen filter, MinClientVersion
2. Hooks + Reporter integration tests — Verify hooks called at correct lifecycle points
3. EventManager concurrency tests — Add/Remove/Dispatch under concurrent load
4. FileTreeEnumerator tests — Blacklist filtering
5. AOT publish verification — dotnet publish -r win-x64 /p:PublishAot=true

Related

• Refactor plan: GeneralUpdate-refactor-plan.md