Function nearest_k_spatial_tensor_parallel_into 

pub fn nearest_k_spatial_tensor_parallel_into<I: ChunkedNearestNeighborIndex + Sync>(
    index: &I,
    x: &[f32],
    y: &[f32],
    z: &[f32],
    tensor: &SpatialTensor<'_>,
    k: usize,
    out: &mut Vec<(usize, Neighbor)>,
)

Parallel k-NN search, appending (query_index, neighbor) pairs to out.