Use postponed evaluation of annotations and type hinting generics in standard collections in Python code

[treiher]

Postponed evaluation of annotations will become the default in Python 3.10:

• https://docs.python.org/3/whatsnew/3.7.html#pep-563-postponed-evaluation-of-annotations
• https://www.python.org/dev/peps/pep-0563/

Type hinting generics in standard collections are supported since Python 3.9:

• https://www.python.org/dev/peps/pep-0585/

Since Python 3.7 both features can be enabled on a per-module basis by adding from __future__ import annotations.