Spoke offline with @xtreak, I'll be sending a PR for this to take over the existing one.

@lisroach proposed a new name, EventMock to differentiate it from any awaitable async notation.

@michael.foord suggested using `mock_timeout` as the argument.

Discussed also to change the naming of the method to `await_until_any_call` to make the semantics similar to the one that `Mock` provides. As `await_until_called_with` might mislead the user that it applies only to the last call.