Merkle tree leaf hashing is done on a larger buffer than necessary

[kobigurk]

The buffer allocated to hash the leaf is larger than the leaf size in order to be able to use the hash_inner_node function: https://github.com/AleoHQ/snarkOS/blob/51b71c1cbd9eec0ccd95016a1b247ce0cd1f2375/algorithms/src/merkle_tree/merkle_tree.rs#L42

While this works for us now in POSW (since Pedersen is homomorphic and the 0s do not change the hash) and using Blake2s (since it works anyway on 512-bit chunks), we might want to change it so there's no confusion in the future.

[howardwu]

What's the status on this?