Add support for Python 3.12. Drop support for Python 3.6 + 3.7.

[rnag]

As Python 3.6 and 3.7 have already past their EOL, I would like to drop library support for those python versions.

Additionally, I will like to add support for Python 3.12 which just released a while back.

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Links:

• https://peps.python.org/pep-0537/#lifespan
• https://docs.python.org/3/whatsnew/3.12.html