message: Use digest instead of sha2 for generality
diff: @@ -2,7 +2,7 @@ use k256::{
  ecdsa::signature::{DigestVerifier, Signature as _}, // traits
  ecdsa::{Signature, VerifyingKey}, // type aliases
  };
  -use sha2::Digest; // trait
  +use digest::Digest; // trait
  use crate::errors::{CryptoError, CryptoResult};
  use crate::identity_digest::Identity256;
  