next.js

a15b974e - [backport]: properly gate segmentCache branch in base-server (#79505)

[backport]: properly gate segmentCache branch in base-server (#79505) In 15.1, this branch should be a no-op when PPR is not enabled, because `collectSegmentData` is [gated](https://github.com/vercel/next.js/blob/69afa37323610c9bbfbecd22f0194f2f299d5a6c/packages/next/src/server/app-render/app-render.tsx#L4008) on `isRoutePPREnabled`. This also sets a no-store cache header when we respond with a 204 to align with intended behavior.