Detect blocking calls in coroutines using BlockBuster

[cbornet]

BlockBuster is a tiny utility to detect blocking calls made in the asyncio event loop during unit tests.
Avoiding blocking calls is hard as these can be deeply buried in the code or made in 3rd party libraries.
Blockbuster makes it easier to detect them by raising an exception when a call is made to a known blocking function (eg: time.sleep).
I opened a PR to integrate BlockBuster in Starlette's tests.
Happy to get your feedback.