refactor(compositor): reduce unnecessary UI updates

- Defer updates when window state hasn't actually changed
- Cache frame-blocked state per screen instead of recalculating constantly
- keep popouts cache so reopening them is instant & clean up otherwise

quickshell/Widgets/DankPopout.qml

@@ -134,12 +134,7 @@ Item {
         }
     }
 
-    Connections {
-        target: CompositorService
-        function onToplevelsChanged() {
-            root._maybeResolveBackend();
-        }
-    }
+    // Backend re-resolution on toplevel activity is covered by CompositorService.frameBlockedByScreen.
 
     function _usesConnectedBackendForScreen(targetScreen) {
         return CompositorService.usesConnectedFrameChromeForScreen(targetScreen);