message: Add to_hex and from_hex for the mockchain key.
diff: @@ -16,6 +16,9 @@ impl PublicKey {
  pub fn from_bytes(bytes: [u8; crypto::PUBLICKEY_SIZE]) -> Self {
  PublicKey(crypto::PublicKey::from_bytes(bytes))
  }
  + pub fn from_hex(string: &str) -> Result<Self, cardano::redeem::Error> {
  + Ok(PublicKey(crypto::PublicKey::from_hex(string)?))
  + }
  }
  /// Private key of the entity.
  @@ -31,6 +34,9 @@ impl PrivateKey {
  pub fn normalize_bytes(xprv: [u8; crypto::PRIVATEKEY_SIZE]) -> Self {
  PrivateKey(crypto::PrivateKey::normalize_bytes(xprv))
  }
  + pub fn from_hex(input: &str) -> Result<Self, cardano::redeem::Error> {
  + Ok(PrivateKey(crypto::PrivateKey::from_hex(&input)?))
  + }
  }
  ///
  