aio.storage timeout type annotation

[djetelina]

aio.storage has timeout defined as int in every type hint, but it falls down through aio.auth, where the type is set correctly (Timeout = Union[aiohttp.ClientTimeout, float]).

[TheKevJames]

This is (somewhat) intentional: as we build both aiohttp-based and requests-based libraries, offering the aiohttp.ClientTimeout as an option outside of gcloud-aio-auth is not intended; rather, the specific http request handling library is meant to be as much of an implementation detail as possible.

That said, since this ticket got opened the build-rest script got a bit better able to handle this sort of polymorphism. I would be open to a PR which allowed users of the various non-auth gcloud-aio libraries to pass through the union of values you specified here, if we can further update that build script to convert it correctly (ie. to just Timeout = float) for gcloud-rest.