New package things

[Zac-HD]

• Get good tests, following the example of flake8-bugbear
• Add typechecking with pyright in strict mode (running via tox)
• [Zac] set up PyPI token and auto-release system

[Zac-HD]

https://pypi.org/project/flake8-trio/ exists 🎉

steps to release:

1. Update the changelog
2. Update the __version__ = number in flake8_trio.py
3. Merge to main and let CI do the work 🚀

@jakkdl let's increment the patch version each time we have a new check or substantial bugfix (i.e. most PRs), the numbers don't cost anything and the sooner code gets to users the more value it adds 😁