Add response handling inside handlers (#80189)
This continues the `handler` signature work from
https://github.com/vercel/next.js/pull/78166 and moves the
cache/response handling work inside of the pages, app pages, and app route handlers which allows them
to be fully invoked independent of `next-server`/`router-server`.
Validated against our deploy tests
https://github.com/vercel/vercel/actions/runs/15583209888/job/43883202911?pr=13433
and
https://github.com/vercel/next.js/actions/runs/15583265934/job/43883389321
