fix!: Reorganize SDK types to tighten helpers around custom props

[blaine-arcjet]

Closes #17

This reworks how some types are represented within arcjet and @arcjet/next to avoid passing rule types deep into the type tree. Instead, we'll now extract the ExtraProps at the SDK type so it no longer looks like Arcjet<Primitive<{}> | Product<{ email: string }>> but instead Arcjet<{ email: string }>. This allows us to tighten the props on withArcjet and createMiddleware because they use the WithoutCustomProps utility.

This is a breaking change to @arcjet/next because I made createMiddleware take the instantiated SDK instead of configuration, which made it easier to adjust these types.

I also took the opportunity to remove some type utility exports because I wanted to rename the EmptyObject for a nicer type error message.

With these changes, this now provides a type error when you try to use protectSignup with the middleware:

[davidmytton]

Can you also open a PR for the docs changes for the new middleware signature please? Then I can test.

[blaine-arcjet]

@davidmytton I've updated the example in this repo. Happy to update the example app and docs once this change is published since doing it before would cause compilation errors.