feat(editor): add blobState$ to BlobEngine (#11756)

Closes: [BS-3137](https://linear.app/affine-design/issue/BS-3137/在-bs-添加-blobstate-接口)

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

## Summary by CodeRabbit

- **New Features**
  - Introduced real-time status tracking for file upload and download operations, allowing users to monitor progress and errors more effectively.
- **Improvements**
  - Enhanced icon display for attachments, providing a refreshed visual experience.
  - Improved update frequency and accuracy for file synchronization status indicators.
- **Bug Fixes**
  - Refined internal logic for filtering status updates, ensuring more precise feedback during file operations.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/framework/sync/src/blob/engine.ts

@@ -104,6 +104,10 @@ export class BlobEngine {
     return key;
   }
 
+  blobState$(key: string) {
+    return this.main.blobState$?.(key) ?? null;
+  }
+
   start() {
     if (this._abort) {
       return;