Typing: always fill in generic type parameters (#2468)

Typing: always fill in generic type parameters (#2468)

* Typing: always fill in generic type parameters

Being explicit about the parameters helps find bugs and makes the library
easier to use for users.

- Tell mypy to disallow generics without parameter values
- Give all generic types parameters values

* fix things that aren't coming in from other commits

* lint

Co-authored-by: Martijn Pieters <mj@zopatista.com>
Co-authored-by: Tom Christie <tom@tomchristie.com>