✨ Add AppendUIDData and CopyUIDData classes

[nevans]

It isn't possible to convert UIDPlusData to use SequenceSet internally, while still maintaining full backwards compatibility. So two new classes were added (AppendUIDData and CopyUIDData). The intention is to remove UIDPlusData in v0.6.0.

• Both AppendUIDData and CopyUIDData:
  • uid-set attributes are SequenceSet objects (not arrays of integers)
  • new validations have been added to the initializers
  • data.size to get the uid-set size
• Only CopyUIDData:
  • uid_mapping => source_uid_to_assigned_uid_hash
    (This behaves identically to the existing UIDPlusData#uid_mapping.)
  • copyuid.assigned_uid_for(source_uid) => assigned_uid
copyuid[source_uid] => assigned_uid
  • copyuid.source_uid_for(assigned_uid) => source_uid
  • copyuid.each_uid_pair (aliases: each_pair, each)

Although they are not perfectly compatible, upgrading from UIDPlusData to CopyUIDData and AppendUIDData should be relatively straightforward.

This PR only adds the classes, but they are unused. For backward compatibility, a parser config option is needed in order to replace UIDPlusData with them. That was split into a separate PR (mostly just to simplify the release notes generation):

• 🔧 Add parser config for APPENDUID/COPYUID, 🗑️ Deprecate UIDPlusData #401

[nevans]

@hoffi Since you submitted the original code, I assume this may affect you. Any thoughts? (See also: #401)

[hoffi]

Looks fine to me 👍