Finalize serialized types for DFGv1

[Affie]

• Breaking changes in serialization from v0.28 to DFG v1 is tracked here and will not be backward compatible until a need for it is identified. We can use converters.
• Persisted (serialized/packed) types shall remain backward compatible during v1.
• Persisted types should be as stable as possible to avoid breaking changes or extra resolvers.
• Adding fields is not a breaking change and therefore we air on the side of caution and rather have less field now.
• Address Clarity of variable names can be improved

See the sub issues for each type.

[Affie]

Fields shared across types

• blobentries
  • I'm good with blobentries.
• metadata
  • The leading idea is that only Blobentry has metadata, the rest will be deprecated for Bloblet, in that case metadata is a good name. Migration difficulty depends on the data type, see Should Blobentry.metadata dict have CRUD? #1172
• bloblets, for the dictionary of Bloblet.
• version - see comment
• timestamp see Change to VariableDFG.missionnanosec alongside .timestamp #1087
• type Type parameter or abstract type information serialized as type::String