Let CompletedFetch have a LogScannerStatus reference

### Search before asking

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


### Description

from: https://github.com/apache/fluss-rust/pull/143#discussion_r2694898471

### Willingness to contribute

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