Fixes #3264 : tests inside @Suite incorrectly classified as flakes

[mirkoalicastro]

When rerunFailingTestsCount is used with JUnit Platform @Suite, tests from different classes that share a method name are merged under the Suite class name. It causes real failures to be misclassified as flakes. With the changes in the PR, findTopParent() now stops at engine boundaries (parents with no ClassSource), correctly attributing tests to their actual class while preserving @Nested.

• New unit test added
• Verified with the small project shared in the original issue: build correctly fails after fix

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[mirkoalicastro]

Hi @olamy , any chance you could have a look at this? 🙏

[mirkoalicastro]

@olamy it looks that there are some failures - unrelated to the changes. Would it be fine to proceed?