message: Use `fold()` when calculating ram Merkle root
diff: @@ -142,18 +142,15 @@ impl IndexedMerkleProof {
  }
  // Compute the raw Merkle root by hashing the proof from leaf hash up.
  - let mut acc = leaf_hash;
  -
  - for hash in hashes {
  + hashes.fold(leaf_hash, |acc, hash| {
  let digest = if (path & 1) == 1 {
  Digest::hash_pair(hash, &acc)
  } else {
  Digest::hash_pair(&acc, hash)
  };
  - acc.0.copy_from_slice(digest.as_ref());
  path >>= 1;
  - }
  - acc
  + digest
  + })
  } else {
  Digest::SENTINEL_MERKLE_TREE
  };
  