Fix AssemblyCleanup running when not all class cleanups might have finished

[Youssef1313]

Fixes #7120

After every test method completes, we marked it as completed.
Then after every class cleanup, we called RunAssemblyCleanupIfNeededAsync, which will check if all tests have been executed, and runs assembly cleanup. This is wrong because all tests could have been executed, but there are remaining class cleanups running in parallel.

This PR updates the logic so we have the concept of "marking test as completed" and "marking test class as completed". Previously we only had the former concept.

[nohwnd]

comments in code.

[Copilot]

Pull request overview

This PR fixes issue #7120 where AssemblyCleanup could run prematurely before all class cleanups had completed in parallel test execution scenarios. The fix introduces a two-stage completion tracking mechanism: marking individual tests as complete, and separately marking entire test classes as complete only after their cleanup methods finish.

Changes:

• Introduced MarkClassComplete method to track when a test class has finished all cleanups
• Modified MarkTestComplete to only indicate when the last test in a class completes, not trigger cleanup
• Updated RunClassCleanupAsync to remove cleanup manager logic and focus on executing cleanup
• Ensured assembly cleanup runs only after all classes are marked complete

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
ClassCleanupManager.cs	Added MarkClassComplete method and refactored MarkTestComplete to return isLastTestInClass flag; removed cleanup execution logic
TestClassInfo.cs	Simplified RunClassCleanupAsync signature by removing ClassCleanupManager and TestMethodInfo parameters and associated logic
UnitTestRunner.cs	Updated to call MarkClassComplete after class cleanup finishes; checks ShouldRunEndOfAssemblyCleanup before running assembly cleanup
UnitTestRunnerTests.cs	Refactored tests to create UnitTestRunner instances per test instead of sharing a field; added helper method CreateUnitTestRunner
ClassCleanupManagerTests.cs	Updated test to use new MarkClassComplete API and removed dependency on TestMethodInfo
AssemblyCleanupTests.cs	Added new integration test verifying assembly cleanup waits for parallel class cleanups with sleep delays