message: add serialization of the BlockHeaders
diff: @@ -312,6 +312,13 @@ impl cbor_event::de::Deserialize for BlockHeader {
  }
  }
  +impl cbor_event::se::Serialize for BlockHeaders {
  + fn serialize<W: ::std::io::Write>(&self, serializer: cbor_event::se::Serializer<W>) -> cbor_event::Result<cbor_event::se::Serializer<W>> {
  + let serializer = serializer.write_array(cbor_event::Len::Len(2))?
  + .write_unsigned_integer(0)?;
  + cbor_event::se::serialize_fixed_array(self.0.iter(), serializer)
  + }
  +}
  impl cbor_event::de::Deserialize for BlockHeaders {
  fn deserialize<'a>(raw: &mut RawCbor<'a>) -> cbor_event::Result<Self> {
  match decode_sum_type(raw)? {
  