fix: removeCells on parent node leaves orphan children causing duplicates

[Copilot]

When removing a parent node via removeCells, its children are not recursively removed from the model, leaving orphan nodes. Subsequent re-creation of nodes with the same IDs results in apparent duplicates.

Root Cause

collection.removeCells sets cell.model = null (via the removed event → onCellRemoved) before calling cell.remove(). Inside remove(), eachChild() calls getChildren() which requires this.model to resolve child IDs — returning null when model is already null. Children are silently skipped.

Changes

• src/model/cell.ts — remove(): Fall back to _children cache when getChildren() returns null due to model being null, ensuring children are still recursively removed:

  const children = this.getChildren() ?? (this._children ? [...this._children] : null)
  if (children) {
    children.forEach((child) => child.remove(options))
  }

• src/model/cell.ts — remove(): Keep parent._children in sync when directly mutating parent.store (bypassing setChildren()), so the fallback cache is not stale.
• __tests__/model/cell.spec.ts: Add test that simulates the actual collection.removeCells flow (model set to null before remove() is called) and asserts children are removed from the model.

Original prompt

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This section details on the original issue you should resolve

<issue_title>🐞3.1.6、3.1.5的删除节点removeCells方法有问题（删除子节点以后，重新创建更新子节点，出现重复节点），3.1.4正常，麻烦排查一下</issue_title>
<issue_description>### 问题描述

🐞3.1.6、3.1.5的删除节点removeCells方法有问题（删除子节点以后，重新创建更新子节点，出现重复节点），3.1.4正常

重现链接

无

重现步骤

🐞3.1.6、3.1.5的删除节点removeCells方法有问题（删除子节点以后，重新创建更新子节点，出现重复节点），3.1.4正常

预期行为

删除节点后，重新创建子节点后，不会出现之前已经删除的节点

平台

谷歌浏览器、mac

屏幕截图或视频（可选但最好有）

No response

补充说明（可选）

No response</issue_description>

<agent_instructions>尝试下找出issue 中问题的原因，并修复。</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@GaoFuhong codesandbox 来个可复现 demo

• Fixes 🐞3.1.6、3.1.5的删除节点removeCells方法有问题（删除子节点以后，重新创建更新子节点，出现重复节点），3.1.4正常，麻烦排查一下 #5032

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.39%. Comparing base (3697830) to head (56249f5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5039      +/-   ##
==========================================
+ Coverage   83.38%   83.39%   +0.01%     
==========================================
  Files         332      332              
  Lines       38487    38498      +11     
  Branches     7898     7905       +7     
==========================================
+ Hits        32093    32107      +14     
+ Misses       6371     6368       -3     
  Partials       23       23              

Flag	Coverage Δ
x6	83.39% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/model/cell.ts	75.40% <100.00%> (+0.46%)	⬆️

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