🐛[BUG]ProFormCascader组件在readonly是label显示错误

ProFormCascader组件在readonly=true时label显示错误，

` [
{
value: 'hangzhou',
label: '浙江',
children: [
{
value: 'hangzhou',
label: '杭州',
children: [
{
value: 'hangzhou',
label: '西湖',
},
],
},
],
},
]}
name="areaList"
readonly={true}
label="区域"
value={['hangzhou', 'hangzhou', 'hangzhou']}
/>`

### 🏞 期望结果
期望显示：浙江/杭州/西湖

Start by reproducing the issue with the provided ProFormCascader example using readonly={true}, the nested area values, and the request data. Inspect the ProFormCascader implementation to find how readonly labels are derived. Done means the displayed value is 浙江/杭州/西湖 for the reported example.

Written by the indexing model from the issue text.