chore: add 3.12 to supported lists

[ooliver1]

Summary

Note
This too relies on #1126 as without poetry, the 3.12 PyPI specifier would have to be added to package metadata as well. This is a draft until that is merged.

Python 3.12 is now stable 🚀. The optimisations are amazing but there's not all too much to benefit from otherwise this time round. Nearly all of the deprecations do not affect us, and there are only module removals (asynchat, asyncore, imp, distutils).

The get_event_loop changes may need some refactoring for both the examples, Client and Webhooks, as that will eventually not create a new loop implicitly (slightly irritating but makes sense).

datetime.datetime.utcnow and datetime.utcfromtimestamp have also been deprecated. This has been solved in #1000 with the DTZ set of rules.

audioop will be removed in 3.13 too, which is used partially in player.py.

The only removals for 3.14 are some deprecations in 3.13 of course.

Don't forget to check the porting section too for behaviour changes in 3.12 for your own bots such as randrange.