Should remove asgiref run-time dependency

[wch]

The asgiref package is used only for types in

py-shiny/shiny/_autoreload.py

Lines 14 to 21 in b458c35

	from asgiref.typing import (
	ASGI3Application,
	ASGIReceiveCallable,
	ASGISendCallable,
	ASGISendEvent,
	HTTPResponseStartEvent,
	Scope,
	)

Since it's not used for anything at run-time, we should remove the run-time dependency and also only import in that file if TYPE_CHECKING.