Draft: Type cleanups

Type cleanups while I'm browsing across (trying to get familiar with) the code base

• Globally turn on PEP 563: Postponed evaluation of annotations
• Not sure which linter we're using yet, but try to delegate this to linters (e.g. isort.required-imports = ["from __future__ import annotations"])
• PEP 585 – Type Hinting Generics In Standard Collections: Use builtin types for annotations