Tighten mypy to disallow-any-generics

[sirosen]

This sets disallow-any-generics = true, which forbids the use of implicit Any in a generic when a type parameter is not provided. There is one troublesome module, related to exception hooks, where this rule is still disabled for now.

The pass over the codebase done here was also used as an opportunity for some minor related refinements, e.g. switching cast usages to type-ignore comments.

• mypy: disallow-any-generics
• Introduce AnyCallable,AnyCommand aliases
• Fix declarations of FieldFormatter[Any]
• Fix usages of bare dict generic type
• Fix any-generics in exception hooks