Use correct generics in routeWithRaise methods

I ran into an issue while integrating Spine into my project (more specifically, the server-arrow module). It seems that the routeWithRaise methods can never apply because of a star-projection in the method signature. Replacing it with Never seems to do the trick.

After adding unit tests to the module (copy/pasted from the server module, but making use of the routeWithRaise method instead of route and raise/ensure instead of fail), I encountered another issue. It seems that declaring failures with the fun <S : FailureSpec> failure(spec: S) overload causes issue when calling the `routeWithRaise` method because it can't seem to resolve the failure back to its original type (for example in the unit tests, an endpoint with the NotFound failure will resolve to a NotFound.Companion but not to a FailureSpec.ByCode<NotFound>, which makes it impossible to use the routeWithRaise for that endpoint).

To solve that second issue I added an overload to the failure which specifically takes a FailureSpec.ByCode<F> as parameter.

I did not find an easier way to make this work, so let me know if you have any suggestions.