refactor(editor): remove unused code (#12142)

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

## Summary by CodeRabbit

- **Refactor**
  - Streamlined internal logic for handling block operations to improve efficiency.
  - Removed unused reactive subject and related code from document handling classes.
  - Renamed a private initialization method for improved clarity.

- **Chores**
  - Cleaned up redundant code and imports to simplify maintenance.

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

blocksuite/framework/store/src/model/store/store.ts

@@ -601,9 +601,7 @@ export class Store {
     this._yBlocks.observeDeep(this._handleYEvents);
     this._yBlocks.forEach((_, id) => {
       this._handleYBlockAdd(id, false);
-    });
 
-    this._yBlocks.forEach((_, id) => {
       if (id in this._blocks.peek()) {
         return;
       }

blocksuite/framework/store/src/test/test-doc.ts

@@ -1,4 +1,3 @@
-import { Subject } from 'rxjs';
 import * as Y from 'yjs';
 
 import type { YBlock } from '../model/block/types.js';
@@ -28,7 +27,6 @@ export class TestDoc implements Doc {
       });
       this.rootDoc.getMap('spaces').set(this.id, subDoc);
       this._loaded = true;
-      this._onLoadSlot.next();
     } else {
       this._loaded = false;
       this.rootDoc.on('subdocs', this._onSubdocEvent);
@@ -39,8 +37,6 @@ export class TestDoc implements Doc {
 
   private _loaded!: boolean;
 
-  private readonly _onLoadSlot = new Subject<void>();
-
   private readonly _onSubdocEvent = ({
     loaded,
   }: {
@@ -54,7 +50,6 @@ export class TestDoc implements Doc {
     }
     this.rootDoc.off('subdocs', this._onSubdocEvent);
     this._loaded = true;
-    this._onLoadSlot.next();
   };
 
   /** Indicate whether the block tree is ready */
@@ -132,7 +127,6 @@ export class TestDoc implements Doc {
 
   private _destroy() {
     this._ySpaceDoc.destroy();
-    this._onLoadSlot.complete();
     this._loaded = false;
   }