Enhanced LanceDB Integration — Vector Indexes, FTS, and Hybrid Search

### Search before asking

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

### Motivation

As discussed in [this](https://github.com/apache/fluss/discussions/2877) thread, we want to enhance the Fluss-LanceDB integration.

Note that for multi vector support, we might need to create a separate FIP because that would need a new datatype in Fluss.

### Solution

Created [FIP-44](https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=429064608)

### Anything else?

_No response_

### Willingness to contribute

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

Start by reading FIP-44 and the linked discussion 2877 to understand the proposed LanceDB integration changes, including vector indexes, full-text search, and hybrid search. The issue does not name implementation files or tests; done means implementing the agreed FIP-44 scope, with multi-vector support handled separately if it requires a new Fluss datatype.

Written by the indexing model from the issue text.