Docs on StructType and EnumType?

[oscartbeaumont]

I think the idea idea was NamedDataType has docs so they don't need it but when it comes to the builder API having it would be useful.

tbh I think we need it on both cause theorically a NamedDataType could be a primitive type and it may want to add docs although this would never be constructed by the Specta macros it's technically something the end-user could declare.