Erase domains types wrapper

[Virgiel]

Our generated domain types do not enforce the domain rules and are only used for ser/deser with the Postgres protocol. By being exposed to the client in parameters and row types, they bring noise without any benefit.

Deserialization

Deserialization is easy, we can simply skip the domain wrapper as it is not needed.

Serialization

We rely on the fact that we generate FromSql ourselves to inject the wrapper at the last minute.

Depends on #73

[LouisGariepy]

Looks good to me! Is this ready to merge?

[Virgiel]

I'm not sure if the domain wrapper type should be in the cornucopia client or in the generated code. I'd like to keep it private as it's only used internally, but copying it every time into the codegen seems silly.

If you are happy with the current design, you can merge !

[LouisGariepy]

That is indeed a good question.

I think we can make it very clear that cornucopia_client is intended to be consumed by tthe generated code, and not something users should depend on. If there are items in cornucopia_client that are intended for users (I think ArrayIterator is one?), then we could move them to a separate cornucopia_utils crate or whatever, intended for advanced users.

What do you think?

[Virgiel]

Another crate may be excessive. How about a core module in the cornucopia client using doc(hidden). This way, the code can be used by our generated code but is hidden from the user. rust-analyzer could even support it in the future.