Automatically convert Tuple-of-future to future-Tuple

[augray]

We already support this for lists:

@sematic.func
def pipeline() -> typing.List[int]:
    return [foo(), bar()]

where foo and bar are Sematic funcs (thus returning futures). We should also support this:

@sematic.func
def pipeline() -> typing.Tuple[int]:
    return (foo(), bar())