refactor(nbstore): improve doc state management (#12359)

Move the `waitForSynced` method from `frontend` to `nbstore worker` to make the wait more reliable

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Added explicit tracking of document updating state to indicate when data is being applied or saved.
  - Introduced new methods to wait for update and synchronization completion with abort support.

- **Improvements**
  - Applied throttling with leading and trailing emissions to state observables for smoother UI updates.
  - Refined synchronization waiting logic for clearer separation between update completion and sync completion.
  - Removed throttling in workspace selector component for more immediate state feedback.
  - Updated import and clipper services to use the new synchronization waiting methods.
  - Simplified asynchronous waiting logic in indexer synchronization methods.

- **Bug Fixes**
  - Enhanced accuracy and reliability of document update and sync status indicators.

- **Tests**
  - Increased wait timeout in avatar selection test to improve stability.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/common/nbstore/src/worker/client.ts

@@ -242,6 +242,10 @@ class WorkerDocSync implements DocSync {
     return this.client.ob$('docSync.docState', docId);
   }
 
+  async waitForSynced(docId?: string, abort?: AbortSignal): Promise<void> {
+    await this.client.call('docSync.waitForSynced', docId ?? null, abort);
+  }
+
   addPriority(docId: string, priority: number) {
     const subscription = this.client
       .ob$('docSync.addPriority', { docId, priority })