Support loaders for script Parameters

[gaborbernat]

Is your feature request related to a problem? Please describe.

For a fanin operation, the arguments are always passed in as json.dumps. We already support loaders for artifacts to map them back to a data structure, would be nice if this could work for parameters too:

class Magic(BaseModel):
    files: list[str]


@script(constructor="runner")
def fan_out() -> Annotated[Magic, Parameter(name="response")]:
    return Magic(files=["1.ok"])

# today we have
@script(constructor="runner")
def fan_in(*, responses: list[str]) -> None:
    values: list[Magic] = [Magic.parse_raw(r) for r in responses]
    print(values)

Describe the solution you'd like

# would be nice if we could have
@script(constructor="runner")
def fan_in(*, responses: Annoted[list[Magic], Parameter(loader=Magic)]) -> None:
    print(responses)

Describe alternatives you've considered
Keep using the transform objects in the first line of your script.

[elliotgunton]

Related: #858 and #827 - better parameter loading is definitely on the roadmap, thanks for the suggestion @gaborbernat!