Bumping the python version

[timurcarstensen]

This PR bumps the python version of the project

I propose that we move the library to python 3.11 (or even better 3.12):

• Python 3.11 (and 3.12) introduced significant performance speedups over previous versions
• PyTorch will soon stop supporting 3.8
• It is easy to bump versions now, when there is still relatively little complexity

For this I have updated .github/workflows/unit-test.yml and setup.py

[timurcarstensen]

Okay final update @aaronkl: we decided to bump the project version to 3.9 and test for 3.9 to 3.11 (including). This is primarily due to this comment regarding the changes to type hinting introduced in 3.9

[aaronkl]

@timurcarstensen thanks for pushing this! Looks good to me. Could you add a sentence to the README that we only support python 3.9 - python 3.11?

[timurcarstensen]

I updated the README.md @aaronkl, could we merge this today?