Improved inference handling for multi types and nargs types

[couling]

There was previously a bug with inference handling where nargs=-1 or multuple=True or is_flag should mean not required, but this was not being assessed. Required inference is now much more reliable.

Type inference handling where nargs=-1 or multiple=True now knows to unbox the tuple[foo, ...] to foo. Likewise inference handling for nargs > 1 also knows to unbox tuple types.

Eg: this now works:

@dataclass
class Foo:
    bar: Annotated[tuple[int, str], argument(nargs=2)]