message: display for chainlength
diff: @@ -89,6 +89,12 @@ impl PartialEq<Self> for KESSignature {
  }
  impl Eq for KESSignature {}
  +impl std::fmt::Display for ChainLength {
  + fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
  + write!(f, "{}", self.0)
  + }
  +}
  +
  impl Header {
  #[inline]
  pub fn block_version(&self) -> AnyBlockVersion {
  