next.js

df247d1b - Move prefetch hints from CacheNodeSeedData to FlightRouterState (#90066)

Move prefetch hints from CacheNodeSeedData to FlightRouterState (#90066) ## Summary Prefetch hints were previously stored in CacheNodeSeedData — the payload the server sends for each segment's React content. This moves them to FlightRouterState, the route tree structure that the server sends alongside the seed data. FlightRouterState is a better home because prefetch hints describe properties of the route structure (loading boundaries, instant configs) rather than properties of the rendered content. It also ensures that hints are always available during navigations, not just prefetches. Since this changes the FlightRouterState tuple layout anyway, it also folds the existing `isRootLayout` boolean and `HasLoadingBoundary` enum into the same bitmask field at FlightRouterState[4]. ## Test plan - Existing unit tests updated for new format (`flight-data-helpers.test.ts`, `types.test.ts`) - MPA navigation test validates root layout change detection via bitmask - `prefetch-true-instant` e2e test validates Link `prefetch={true}` behavior with instant routes