Allow positional parameters for a collection to be passed without a name#61

Given ```python # adder1.py from clipstick import parse from pydantic import BaseModel class Adder(BaseModel): ints: int def run(self): print(sum([self.ints])) cmd = parse(Adder) cmd.run() ``` this runs OK: ```bash $ adder1.py 10 10 ``` but this ```python # adder2.py from clipstick import parse from pydantic import BaseModel class Adder(BaseModel): ints: list[int] def run(self): print(sum(self.ints)) cmd = parse(Adder) cmd.run() ``` fails for multiple arguments: ```bash $ adder2.py 10 20 ERROR: Missing a value for positional argument '--ints' ``` and requires ```bash $ adder2.py --ints 10 --ints 20 30 ``` It would be desirable that positional arguments for a collection could be passed just as values.