[Umbrella] Subissue Improve memory.* test coverage

### Search before asking

- [x] I searched in the [issues](https://github.com/alibaba/fluss/issues) and found nothing similar.

### Description

Currently, we ignore a lot of classes to make the code coverage pass. We need to add unit tests or integration tests around those classes to improve the coverage.
In this issue, it aims to cover com.alibaba.fluss.memory.* to increase the coverage.

### Willingness to contribute

- [ ] I'm willing to submit a PR!

Start by locating the com.alibaba.fluss.memory.* package and checking which classes are currently ignored by coverage. Add unit or integration tests around those classes, then run the relevant test suite and coverage checks to confirm that coverage improves.

Written by the indexing model from the issue text.