Add initial flake8-trio rule (#8439)
## Summary
This pull request adds
[flake8-trio](https://github.com/Zac-HD/flake8-trio) support to ruff,
which is a very useful plugin for trio users to avoid very common
mistakes.
Part of https://github.com/astral-sh/ruff/issues/8451.
## Test Plan
Traditional rule testing, as [described in the
documentation](https://docs.astral.sh/ruff/contributing/#rule-testing-fixtures-and-snapshots).
