fix: render group title for single-column lists

[biubiukam]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• TypeScript definition update
• Bundle size optimization
• Performance optimization
• Enhancement feature
• Refactoring
• Update dependency
• Code style optimization
• Test Case
• Branch merge
• Site / documentation update
• Demo update
• Workflow
• Chore
• Release
• Other (about what?)

🔗 Related issue link

fix #5014

💡 Background and solution

When ListTable uses groupConfig with only one data column, parent group rows still carry vtableMerge group-title data, but their merge range collapses to a single cell. The renderer previously entered the group-title rendering path only when the range spanned multiple cells, so the parent group row could render blank.

This change treats vtableMerge rows as group-title cells even when the merge range is a single data cell, while still excluding row series cells. It also avoids the normal fast text update path for those group-title cells so groupTitleFieldFormat is applied.

A regression test was added for a grouped ListTable with one data column to verify the parent group title is rendered.

📝 Changelog

Language	Changelog
🇺🇸 English	Render group title rows correctly for grouped ListTable with only one data column.
🇨🇳 Chinese	修复 ListTable 分组表在仅有一个数据列时父分组标题行空白的问题。

☑️ Self-Check before Merge

⚠️ Please check all items below before requesting a reviewing. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

---

🚀 Summary

copilot:summary

🔍 Walkthrough

copilot:walkthrough