feat: Move prftree into ciphers crate

- Use a new nomenclature for these functions based on the idea of a hash
  domain (as in domain separation); this makes much more sence
- Remove the ciphers::hash export; we did not even export a hash
  function in the purest sence of the word. This gets us around the
  difficulty of figuring out what we should call the underlying
  primitive

ciphers/Cargo.toml

@@ -14,5 +14,6 @@ anyhow = { workspace = true }
 rosenpass-sodium = { workspace = true }
 rosenpass-to = { workspace = true }
 rosenpass-constant-time = { workspace = true }
+rosenpass-secret-memory = { workspace = true }
 static_assertions = { workspace = true }
 zeroize = { workspace = true }