[Bug]: legend 配置 maxCols 未生效

### Describe the bug / 问题描述

```
import { Chart } from '@antv/g2';

const chart = new Chart({ container: 'container', height: 350 });
const shapeList = ['bowtie', 'smooth', 'hv', 'rect', 'hollowPoint'];
const data = [
{ genre: 'Sports', sold: 50 },
{ genre: 'Strategy', sold: 115 },
{ genre: 'Action', sold: 120 },
{ genre: 'Shooter', sold: 350 },
{ genre: 'Other', sold: 150 },
];
chart.options({
type: 'interval',
data,
encode: { x: 'genre', y: 'sold', color: 'genre' },
legend: {
color: {
maxCols: 1
},
},
});

chart.render();
```

### Reproduction link / 复现链接

(https://g2.antv.antgroup.com/manual/component/legend#%E9%85%8D%E7%BD%AE%E9%A1%B9)

### Steps to Reproduce the Bug or Issue / 重现步骤


### Version / 版本

Please select / 请选择

### OS / 操作系统

- [x] macOS
- [ ] Windows
- [ ] Linux
- [ ] Others / 其他

### Browser / 浏览器

- [x] Chrome
- [ ] Edge
- [ ] Firefox
- [ ] Safari (Limited support / 有限支持)
- [ ] IE (Nonsupport / 不支持)
- [ ] Others / 其他

Start with the legend configuration documentation and the supplied Chart reproduction. Trace how the color legend reads maxCols, then verify the example with maxCols set to 1. Done means the legend layout visibly respects that setting in the reproduced chart.

Written by the indexing model from the issue text.