Introduce CompactedKeyEncoder

### Search before asking

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


### Description

as title. Please refer to java implementation https://github.com/search?q=repo%3Aapache%2Ffluss%20CompactedKeyEncoder&type=code

### Willingness to contribute

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