preserve allowQuery for partial fallback shells (#90887)
Analogous change to https://github.com/vercel/vercel/pull/15338, but for the new Next.js adapter API.
This updates only allowQuery for fallback HTML when the route is a true partialFallback (PPR fallback with postponed state) and cache components is enabled. For all other fallback cases, behavior stays the same as today (allowQuery is cleared to [] for shared fallback caching).
This change is needed because partial-fallback shells can be param-specific, so collapsing them to one shared fallback cache key can serve the wrong shell across params and block correct upgrade behavior. Gating this behind partialFallback lets us roll out the new behavior safely and independently, without changing legacy fallback semantics for non-partial paths.
