python3.13 support

[jakkdl]

I noticed that ci.yml doesn't list 3.13 in the test matrix, it should be added and classifiers in setup.py updated (and any problems fixed).

And while perusing that file I noticed this comment is outdated

trio-websocket/.github/workflows/ci.yml

Lines 15 to 16 in e7706f4

	# latest pylint/astroid doesn't support 3.7
	# python3.7 is covered in build_and_test_old_deps

3.7 isn't tested/supported at all, so we can probs just remove that comment straight up.

We're also closing in on 4 months since EOL of 3.8, but I don't think we're in any rush to drop that