increase minimum python version to 3.10

[andlaus]

most importantly, this will allow us to use kw_only for dataclasses and thus significantly simplify "manual" object creation
(because with kw_only dataclasses, it is possible to use defaulted attributes and class inheritance simultaneously)

currently, this is blocked by the fact that we aim for all maintained Ubuntu LTS releases to be supported out of the box. The first release that ships with python >= 3.10 is 22.04, i.e., until Ubuntu 20.04 reaches its end of life in April 2025, we are stuck with python 3.8...

[andlaus]

• use the build-in container types (dict, list, ...) instead of the ones imported from typing for type annotations
• for type annotations, use | instead of typing.Union to express multiple possibilities