[Persisted] Make broadcast subscriptions granular by key (#4874)

* Add fast path for guaranteed noop updates

* Change persisted.onUpdate() API to take a key

* Implement granular broadcast listeners

src/state/preferences/large-alt-badge.tsx

@@ -26,9 +26,12 @@ export function Provider({children}: React.PropsWithChildren<{}>) {
   )
 
   React.useEffect(() => {
-    return persisted.onUpdate(() => {
-      setState(persisted.get('largeAltBadgeEnabled'))
-    })
+    return persisted.onUpdate(
+      'largeAltBadgeEnabled',
+      nextLargeAltBadgeEnabled => {
+        setState(nextLargeAltBadgeEnabled)
+      },
+    )
   }, [setStateWrapped])
 
   return (