Function collect_representatives 

pub fn collect_representatives(
    store: &ReadableWritableListableStorage,
    source: &EmbeddingsSource,
    selected_ids: &Array1<u32>,
    fallback_batch_vecs: usize,
    memory_limit_bytes: usize,
    chunk_shape: &[u64],
    dtype: EmbeddingDtype,
) -> Result<()>

Saves the chosen representatives into the index. Copies the rows of source listed in selected_ids, which must be sorted ascending. Reads whole chunks and skips any chunk with no selected row.