finalize python39 transition

Description

Fix python required version and replace deprecated imports from typing module

Related Issues

Related to #24 (closed)

Type of Change

• change the required python version
• replace deprecated imports from typing module based on https://peps.python.org/pep-0585/#implementation

Potential side effects

Screenshots / GIFs (if applicable)

Additional Comments

With python/3.9 it's preferred to use built-in collection types such as list and dict as generic types instead of importing the corresponding capitalized types (e.g. List or Dict) from typing: https://docs.python.org/3/whatsnew/3.9.html#type-hinting-generics-in-standard-collections

Definition of Done

• Documentation is up-to-date.