`DeriveValueType` proc macro relies on several sea-orm types to be
imported. This is partially fixed in #1855 by fully qualifying
`sea_orm::QueryResult`, but others like `sea_orm::Value` is still not
being qualified. Also, if use defined a type alias on
`std::result::Result`, it can cause the proc macro to generate code that
won't compile.
- Fully qualify `sea_orm::Value`, `std::string::String`, and
`std::result::Result` in `DeriveValueType` proc macro.
- Add some simple integration tests for this.
- Add doc and doc test in `sea_orm_macro::derive_value_type`.