Plans with positional only args cannot be run

[tpoliaw]

Given a plan such as

def demo(foo: int, /, bar: int) -> MsgGenerator:
    yield from ()

due to the method of wrapping all arguments into a dict and passing as demo(**args), it doesn't appear to be possible to run this plan.

This might not be an issue but if it's not intended to be supported, it would be good to document that somewhere and maybe warn when the plans are being read/registered.

[callumforrester]

Thanks, no strong opinion on whether to support or just document