deprecate python 3.9 support

[bmw]

fixes #239. this PR was based on #194

[ohemorange]

lgtm. seeing #194 (comment); was that further deprecations that should go out in those release as well?

[bmw]

i don't think so. grepping the code for various versions of references to python 3.9 and 3.10, i'm not seeing anything else that should be done when we drop python 3.9 support like there was when we dropped python 3.8

if you think i'm missing something tho, plz lmk!

[ohemorange]

also not sure what that comment was referring to, as we don't seem to currently depend on importlib_resources anywhere here -- looks like it was removed when 3.8 was. 37f6889

[bmw]

my understanding of #194 (comment) is i was saying that i started trying to remove importlib_resources in that PR which was deprecating but not removing python 3.8 support, but then realized it's not going to work until we drop python 3.8 support entirely so i forced pushed to that PR to remove the premature commits

i then did actually go through with removing importlib_resources in the PR that completely removed python 3.8 support which was #214 which was squashed into 37f6889

and in the case of this PR here deprecating but not removing python 3.9 support, i'm not seeing any additional code we can clean up when we go to fully remove python 3.9 support in a later PR

hopefully that makes more sense?

[ohemorange]

great, that matches my understanding. I wasn't sure if that ended up happening in a follow-up PR and needed to happen now, but then I found it.