message: add header deser test
diff: @@ -98,7 +98,7 @@ impl Header {
  }
  }
  -#[derive(Debug, Copy, Clone)]
  +#[derive(Debug, Copy, Clone, PartialEq, Eq)]
  pub(crate) struct U128Header {
  pub num_vals: u32,
  pub codec_type: U128FastFieldCodecType,
  @@ -285,6 +285,18 @@ pub fn serialize_and_load<T: MonotonicallyMappableToU64 + Ord + Default>(
  mod tests {
  use super::*;
  + #[test]
  + fn test_serialize_deserialize_u128_header() {
  + let original = U128Header {
  + num_vals: 11,
  + codec_type: U128FastFieldCodecType::CompactSpace,
  + };
  + let mut out = Vec::new();
  + original.serialize(&mut out).unwrap();
  + let restored = U128Header::deserialize(&mut &out[..]).unwrap();
  + assert_eq!(restored, original);
  + }
  +
  #[test]
  fn test_serialize_deserialize() {
  let original = [1u64, 5u64, 10u64];
  