Function parallel_topn_vector_search 

pub fn parallel_topn_vector_search(
    rows: RowVec,
    vector_col_idx: usize,
    query_bytes: &[u8],
    k: usize,
    metric: DistanceMetric,
    config: &ParallelConfig,
) -> Result<Vec<(i64, Row, f64)>>

Parallel brute-force k-NN vector search

Fuses distance computation + top-K heap selection into parallel chunks, then merges chunk heaps. Zero-copy on Extension(Vector) values.

Returns (row_id, row, distance) sorted by distance (ascending).