Add JSDoc based types

[wooorm]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

This adds types through JSDoc comments.

I’m raising this as a PR because it does not use generics, which are available in the current .d.ts, which seem quite useful in u. Maybe the JSDoc can be improved, or this is a case where a .d.ts file is preferred