Look into using ZookeeperTestingServer to test ZooCache

In the following comment an experimental IT was written to test ZooCache performance.

https://github.com/apache/accumulo/issues/5040#issuecomment-2465200143_

While that performance test would not be suitable for an IT, it may be good to write an IT that test ZooCache correctness in a similar way to that test. There is a fairly extensive zoo cache unit test that uses mocking. It would be better to move a subset of those test to use a real zookeeper. That unit test assumes that when a node has zero children in zookeeper that null is returned which is not the case see #5047. The ZookeeperTestingServer is really fast so running the test would not take longer, but the test would be more accurate than mocking.

Start by locating the existing ZooCache unit test and read the experimental integration test described in the comment on #5040. Identify a focused subset of mocked correctness tests that can run against ZookeeperTestingServer, accounting for the zero-children behavior noted in #5047. Done means the selected checks run as an integration test against real ZooKeeper and verify ZooCache correctness.

Written by the indexing model from the issue text.