Stop supporting python3.8

[niksirbi]

Python 3.9 introduced type hinting generics in standard collections via PEP 585.
This allows us to directly use the usual Python collection types (eg list, dict) as type hints, instead of using typing.List and typing.Dict. Moreover, even though typing collections still work as type hints on newer Python versions, they are being deprecated.
The solution is to get rid of Python 3.8, the active support of which has already ended (with security support ending in ~1 year, see endoflife.data).

[niksirbi]

Issue was raised by @lochhh while reviewing PR #33.

[lochhh]

We would still need typing.Optional and typing.Union in load_poses.py with 3.9, since the | syntax is only supported 3.10 onwards.

[niksirbi]

Hm, that's annoying, it's too early to get rid of Python 3.9 yet. We have to tolerate typing.Optional and typing.Union for now.
But we can still get rid of Python3.8 and start using the "usual" collections in type hints. Solving half the problem is still worth it?

[lochhh]

Yep definitely stick with 3.9+ for now - can imagine other dependencies still requiring at least 3.9

[adamltyson]

Yep definitely stick with 3.9+ for now - can imagine other dependencies still requiring at least 3.9

I'm keen to stick to NEP29 where we can.

[niksirbi]

@DhruvSkyy has kindly volunteered to have a shot at this one 🍾

[niksirbi]

closed via #54