Function respond_to_message 

pub fn respond_to_message<O, M, N, S>(
    root: &N,
    object_store: &S,
    msg: &Message<M, O>,
    threshold: usize,
    split: fn(usize) -> Vec<usize>,
) -> Result<(Message<M, O>, Vec<O>), RespondError<M>>
where
    M: ProtocolMonoid,
    for<'de2> O: Object<M::Item> + Serialize + Deserialize<'de2>,
    S: ObjectStore<M::Item, O>,
    N: Node<M>,
    for<'de2> M::Item: Serialize + Deserialize<'de2>,
    for<'de2> M::Encoded: Serialize + Deserialize<'de2>,