🤔为什么明细表底部要有一个空白区域占位

### 🏷 Version

| Package | Version |
| -------------- | ------- |
| @antv/s2 | 2.0.0-next.31 |
| @antv/s2-react | - |
| @antv/s2-vue | - |

### Sheet Type

- [ ] PivotSheet
- [x] TableSheet
- [ ] GridAnalysisSheet
- [ ] StrategySheet
- [ ] EditableSheet

### 🖋 Description

为什么明细表底部要有一个空白区域占位？一开始我以为是给横向滚动条预留的位置，但是就算我增加列数到出现横向滚动条，底部还是固定有一小行空白

### 🔗 Reproduce Link

基础明细表 | S2
https://s2.antv.antgroup.com/examples/basic/table/#table

### 😊 Expected Behavior

### 😅 Current Behavior

Start with the TableSheet example at https://s2.antv.antgroup.com/examples/basic/table/#table and reproduce the fixed blank area below the detail table, both with and without a horizontal scrollbar. Trace the TableSheet layout from that entry point; done means the unnecessary bottom space is removed or its purpose is clearly resolved without breaking scrolling.

Written by the indexing model from the issue text.