Fix typing for async route methods

[wsanchez]

Add some async methods to typing_app.py to verify that those work… and they do not:

src/klein/test/typing_app.py:87:6: error: Value of type variable "KleinRouteHandlerT" of function cannot be
"Callable[[Application, IRequest], Coroutine[Any, Any, Union[Union[Union[str, bytes, IResource, IRenderable, Tag, None], Iterable[Union[str, bytes, IResource, IRenderable, Tag, None]]], Awaitable[Union[Union[str, bytes, IResource, IRenderable, Tag, None], Iterable[Union[str, bytes, IResource, IRenderable, Tag, None]]]]]]]"
 [type-var]

These errors are a bit tough to read… I gave it a stab but I'm not sure why this is unhappy.

[glyph]

I think this file might not be a great idea for testing types; we should have most of this type stuff covered by annotated tests. But in any case I have some comments inline about what these type signatures should be.

[glyph]

-> KleinRenderable isn't doing what you think here, because KleinRenderable includes both KleinSynchronousRenderable and Awaitable[KleinSynchronousRenderable], and you can't return both of those here; due to the implicit modification of async def, the actual return type of this function becomes (handwaving a bit over the Coroutine junk) Awaitable[Union[KleinSynchronousRenderable, Awaitable[KleinSynchronousRenderable]], which is gibberish.

What you actually want to do with these methods is to say, for example, "-> str", which will implicitly match against -> KleinRenderable.

[wsanchez]

OK that works for cases where I know the specific type I'm returning. What if I'm returning the result of something that gives me a KleinRenderable?

Presumably I will have awaited on it if appropriate, so I agree that maybe this should be KleinSynchronousRenderable, though that's currently not public.

That is, it should be possible to type this generically.

[wsanchez]

If I use KleinSynchronousRenderable, I at least get passing for these, but it doesn't catch asyncReturnsObject as invalid… so not perfect, but better.