simplify conversion traits and wrapper types

[arcnmx]

Compile times seem to kind of blow up with too many generic impls, and it's not always worth the convenience.

• consider a Wrapper<Type> type to replace any TypeWrapper structs
  • double-check that all Wrapper structs always name their single field data
• impl explicit conversions to TypeWrapper rather than using complicated blanket impls.
  • IntWrapper: i32 i16 i8 u16 u8
  • StringWrapper: String Box<str> Cow<str> &str char
  • Type assuming a generic wrapper struct
• forget about obscure impls for structs with a base plus optional fields
• the tuple to enum conversions are likewise just as silly
• reconsider how to handle types that have a base and nothing else
  • as well as a base and all optional fields

Not all of this necessarily relates to performance, but in general the idea is to be a bit more conservative for the sake of simplicity.