add unstable_prefetch config to typescript plugin (#83181)
In #8290 i forgot to update our typescript plugin, so exporting
`unstable_prefetch` caused it to error.
This is fixed now:
<img width="871" height="145" alt="Screenshot 2025-08-28 at 17 19 18"
src="https://github.com/user-attachments/assets/ca295029-5a93-483b-8f2b-2f821c452397"
/>
<img width="841" height="176" alt="Screenshot 2025-08-28 at 17 19 29"
src="https://github.com/user-attachments/assets/414b18f8-c3c0-46fd-acd0-25b04a85fbd2"
/>
I've also added some type safety to the `options` objects that we
specify there to make sure they're in sync with the values they
describe.
