[MAINT] run tests with all python >=3.9

[Remi-Gau]

• drop python<3.8
• support all python >= 3.9: test in CI

[Remi-Gau]

will rebase on main once #5 is merged

[tsalo]

lol you figured out the problem so much faster than me. I think the type annotations with | require at least Python 3.10 though.

[Remi-Gau]

na adding from __future__ import annotations at the top of the module should be fine

[tsalo]

Oh cool! I'll put that in my PR then.