Separate package for `asgiref/typing.py`

[relsunkaev]

For those who just want to use this library for typing their ASGI apps/servers (namely uvicorn and starlette), it doesn't make much sense to depend on the entirety of this package just for the types. Would you be open to splitting out the types into a separate package (django/asgitypes perhaps?) and have asgiref depend on that instead? That way package maintainers are more incentivized to type their packages and, possibly, adhere to the spec more closely.

[Kludex]

I've created https://github.com/Kludex/asgi-types for the time being.

I'm willing to transfer the repository to django if wanted.

[adriangb]

+1 to this, I think it would be a good move for the ecosystem in general and a backwards compatible change for asgiref.