in src/node_template.rs [52:57]
fn merge(lch: &HashNodeSmt<D>, rch: &HashNodeSmt<D>) -> HashNodeSmt<D> {
let mut hasher = D::new();
hasher.update(&lch.hash);
hasher.update(&rch.hash);
HashNodeSmt::new(hasher.finalize().to_vec())
}