[Feature](lance) Add radius and full-text search modes

[Gabriel39]

Parent

Tracked by #66340. ANN and Flat vector search were introduced by #65730.

Scope

• Add Radius/Range Search with lower and upper distance bounds.
• Add standalone full-text search with BM25.
• Define result schemas, filtering order, scoring semantics, limits, and EXPLAIN output.
• Keep Hybrid Search out of scope unless it is designed separately.

Completion criteria

• FE analysis and BE/lance-c execution paths are implemented.
• Unit and regression tests cover bounds, BM25 scoring, filters, and invalid parameters.
• User documentation describes syntax, score or distance semantics, and limitations.
• Representative indexed and non-indexed datasets are verified.