🐛 Fix Python3.11+ raises ModuleNotFoundError: No module named typing_extensions

[waketzheng]

How to reproduce:

mkdir temp
cd temp
python3.11 -m venv venv
source venv/*/activate
pip install asyncer
python -c 'import asyncer'

BTW: I changed anyio.sleep(0) to anyio.lowlevel.checkpoint as ruff check --extend-select=ASYNC suggested. And remove the file poetry.toml as no longer need it.

[github-actions]

📝 Docs preview for commit 87df3b9 at: https://972dccbd.asyncer.pages.dev

[waketzheng]

@tiangolo How to add a label?

[Stealthii]

This bug affects v0.0.8 (the latest version) only.