Private Merkle Treaps shouldn't leak information through hashes

[Nuhvi]

For the eventual work on e2e encrypted (private) repos, hashes like the rank (hash of the key) or hashes of the node might leak some private information, for example there would be a globally well-known rank for the key bitcoin wallet backup, to avoid this, we should mix the encryption key (or a hash of it) with all hashing operations, so instead of rank = hash(key) it should be rank = hash(key | encrypitonKey) or rank = hash(key | hash(encryptionKey))