FR: Loosen bound on merkle tree inputs from &[Vec<u8>] to &[impl AsRef<[u8]>]

[preston-evans98]

Description

Change the API of MerkleHash::hash_byte_vectors and simple_hash_from_byte_vectors to accept &[impl AsRef<[u8]>] as an argument instead of only &[Vec<u8>]. This will allow consumers to hash borrowed data, avoiding unnecessary copies.

Definition of "done"

The APIs of both functions have been updated.

pub fn simple_hash_from_byte_vectors<H>(byte_vecs: &[impl AsRef<[u8]>]) -> Hash
where
    H: MerkleHash + Default,
{
    let mut hasher = H::default();
    hasher.hash_byte_vectors(byte_vecs)
}

pub trait MerkleHash { 
    // ...
    fn hash_byte_vectors(&mut self, byte_vecs: &[impl AsRef<[u8]>]) -> Hash {
        let length = byte_vecs.len();
        match length {
            0 => self.empty_hash(),
            1 => self.leaf_hash(byte_vecs[0].as_ref()),
            _ => {
                let split = length.next_power_of_two() / 2;
                let left = self.hash_byte_vectors(&byte_vecs[..split]);
                let right = self.hash_byte_vectors(&byte_vecs[split..]);
                self.inner_hash(left, right)
            },
        }
    }
    }