Function append_node_batch 

pub fn append_node_batch(
    store: &ReadableWritableListableStorage,
    group_path: &str,
    child_key: &str,
    embeddings: &Array2<f32>,
    children: &Array1<u32>,
    chunk_shape: &[u64],
    dtype: EmbeddingDtype,
) -> Result<()>

Appends embeddings and their children ids to the node at group_path, creating its arrays on the first call; the ids go in child_key (node_ids or item_ids). border is left at its fill value, never populated.