Throttle notification state calculation (#31922)

Because every room in a space will emit a notification state change
when push rules change so we would otherwise recalculate the space
notification state for every room in the space, On^2 style.

src/stores/notifications/SpaceNotificationState.ts

@@ -6,6 +6,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
+import { throttle } from "lodash";
 import { type Room } from "matrix-js-sdk/src/matrix";
 
 import { NotificationLevel } from "./NotificationLevel";
@@ -63,7 +64,8 @@ export class SpaceNotificationState extends NotificationState {
         this.calculateTotalState();
     };
 
-    private calculateTotalState(): void {
+    private calculateTotalState = throttle(
+        (): void => {
             const snapshot = this.snapshot();
 
             this._count = 0;
@@ -81,5 +83,8 @@ export class SpaceNotificationState extends NotificationState {
 
             // finally, publish an update if needed
             this.emitIfUpdated(snapshot);
-    }
+        },
+        100,
+        { leading: false, trailing: true },
+    );
 }