using Container.get on async factories leads to confusing behaviour

[elfjes]

async factories are supposed to be invoked using await Container.aget. However, currently there's nothing stopping a user from using the normal Container.get method. For example, this works for an async factory:

async def int_factory():
    await asyncio.sleep(0)
    return 42

registry.register_factory(int, int_factory)
await container.get(int) # obtains 42 even though the sync .get method was used

A user that doesn't know about aget might think all is well. But all is not well, since the value stored in the container is not 42 but the coroutine, which has now been awaited.

Solution could be to detect if .get is used for an async factory and raise an error. Luckily there already is the RegisteredService.is_async flag to help out with that

[hynek]

fix is in 23.11!