Small changes requiring serialization changes to implement

[AloeareV]

          I am confused about the presence of both `u64` and `u32` for..  ?similar? fields.
          
          Is the regression proptest data because of this variance?  Is it correct?

Originally posted by @zancas in https://github.com/zingolabs/zingolib/pull/992#pullrequestreview-2021431681

This needs a serialization version increment to align, (and handling for if we somehow read a None), which is fiddly and we likely don't have time for before zip317.

This would be a good place to keep track of anything else that necessitates a version bump, in case we can do multiple changes at once and make the versioning simpler.