Close contexts when clearing test context cache

[Will-thom]

This updates the TestContext Framework cache so that clearing the cache also closes cached ConfigurableApplicationContext instances instead of only dropping the internal references. The implementation reuses the existing removal path, preserving the hierarchy-aware close behavior already used by cache eviction/removal.

The ContextCache contract now documents the close behavior for clear(), and LruContextCacheTests covers both clear() and reset(), since reset() delegates to clear().

Closes gh-26196

Tests:

• ./gradlew.bat --no-daemon --max-workers=1 :spring-test:test --tests org.springframework.test.context.cache.LruContextCacheTests
• ./gradlew.bat --no-daemon --max-workers=1 :spring-test:test --tests org.springframework.test.context.cache.ContextCacheTests
• ./gradlew.bat --no-daemon --max-workers=1 :spring-test:check

[sbrannen]

Thanks for the PR, @Will-thom. 👍

Closes gh-26196

Please note that this change would only serve as a building block for #26196, since it would not address the broader topic raised in that issue.

In any case, it makes sense for clear() and reset() to actually close contexts instead of just removing them from the cache.

Also, please make sure you comply with the DCO requirement by signing your commits. Otherwise, we cannot process this PR.

[sbrannen]

@Will-thom, please address the DCO sign-off issue.

There is one commit incorrectly signed off. This means that the author of this commit failed to include a Signed-off-by line in the commit message.

To avoid having PRs blocked in the future, always include Signed-off-by: Author Name authoremail@example.com in every commit message. You can also do this automatically by using the -s flag (i.e., git commit -s).