[Feature]: Support npm package names in `setupFiles`

### What problem does this feature solve?

setupFiles should accept npm package names in addition to local file paths.

This matches Vitest and Jest behavior and allows loading setup utilities directly without wrapper files.

### What does the proposed API look like?

Example:

```js
setupFiles: [
  '@scope/my-rstest-config/setup',
  './test/setup.ts',
]
```