Minimal structural view of a TanStack Query result - the signal-bag fields
fromQuery reads.
A CreateQueryResult<T> from @tanstack/angular-query-experimental
satisfies this shape (its status / fetchStatus / data / error are
all Signals), so the adapter stays decoupled from TanStack's experimental
proxy typing while still accepting a real query result directly.
Optional TanStack dataUpdatedAt (epoch ms; 0 = no successful load
yet). When bound, it feeds lastUpdated and makes the first-load latch
exact - placeholder data does not bump it, so a placeholder-backed query
still counts as first load.