Redirect for subrouters

Commented [here](https://github.com/go-chi/chi/issues/709), but since the issue cannot be reopened, I opened this issue to continue the discussion.

Copy of my comment there:

> I'm not sure whether my question relates to the initial question, but perhaps it makes sense when subrouters are used? Consider this:
> ```
> router.Route("/{username}", func(r chi.Router) {
> r.Get("/", func(w http.ResponseWriter, request *http.Request) {
> // r.Redirect("/details") <---- This is where I want to redirect to, keeping the subrouter's prefix (/{username}).
> })
>
> r.Get("/details", func(writer http.ResponseWriter, request *http.Request) {
> // ... <---- Redirects here
> })
> }

_Originally posted by @shamilovstas in [#709](https://github.com/go-chi/chi/issues/709#issuecomment-2888496580)_

Start by reviewing the linked issue #709 and the shown router.Route and r.Get entry points; no source file or test is named in this issue. Define whether a redirect API should preserve the subrouter prefix, and consider the request complete only when that behavior is specified and covered by an agreed implementation and test.

Written by the indexing model from the issue text.