[Umbrella] Subissue Improve kv.* 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.kv.*` to increase the coverage.

### Willingness to contribute

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

The issue targets the com.alibaba.fluss.kv.* package but names no specific files, tests, or entry points. Begin by inventorying the ignored classes and existing unit or integration coverage, then determine which tests are needed for the package to be covered and verify the resulting coverage increase.

Written by the indexing model from the issue text.