Add positional-only / keyword-only check to pr-review skill (#194099)

## Author Notes

Realized that the skill was missing these.

## Agent Notes

> Adds one item to the API Design section of the pr-review skill's checklist:
> new public APIs and internal functions should use `/` and `*` in their
> signatures rather than leaving every argument positional-or-keyword.
>
> The rationale is the asymmetry: either marker can be dropped from a signature
> later without breaking a single caller, but neither can be added later, so the
> strict form has to be picked when the API is introduced. The item notes that
> historical APIs don't follow this, so it applies to new signatures only.
>
> An earlier draft of this item also told reviewers to put the leading tensor
> argument before `/`. That was wrong and was removed: `torch.add(input=t,
> other=t)` and `torch.sum(input=t)` both work, so `input` is a documented,
> keyword-passable parameter across `torch.*`.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/194099
Approved by: https://github.com/janeyx99