message: Update the changelog re: packed/transparent reprs
diff: - `Error` now implements `From<Infallible>`, which allows passing convertible
  extents (like tuples of integers) where `impl TryInto<Extents>` is required.
  - Support for HDF5 versions 1.12.1 and 1.10.8
  +- `#[derive(H5Type)]` now supports structs / tuple structs with `repr(packed)`.
  +- `#[derive(H5Type)]` now supports structs / tuple structs with
  + `repr(transparent)` (the generated HDF5 type is equivalent to the type of
  + the field and is not compound).
  ### Changed
  