fix: Refine async_timeout to properly handle TypeVar usage

[filipchristiansen]

This PR updates the async_timeout function signature to address a Pylance warning about TypeVar usage. Specifically, the function definition has been changed from:

-def async_timeout(seconds: int = 10) -> Callable[..., Callable[..., Awaitable[T]]]:
+def async_timeout(seconds: int = 10) -> Callable[[Callable[..., Awaitable[T]]], Callable[..., Awaitable[T]]]: