[Feature] 树形表格， extensionRows形式扩展的行列，支持自定义表头及单元格

What problem does this feature solve?

在 https://visactor.com/vtable/demo/table-type/pivot-table-multi-tree 基础上，扩展出实现一个带合并单元格及树形节点的表格demo, 期望能针对节点自定义。

实现基础： extensionRows能力（如果有其他方式能实现如下效果也可以替代）

简单代码例子：
`
const useData = [
{
"group0": "111",
"group1": "Ouput",
"group2": "1",
"METRIC": "test111",
"unit": "个",
// "State": "test111-2221", 汇总行数据，需要去除子节点临时标识
"DIMENSION_1": "456",
"DIMENSION_2": "457",
rowId: 1,
},
{
"group0": "111",
"group1": "Ouput",
"group2": "1",
"METRIC": "test111",
"unit": "%",
"State": "test111-2221",
"DIMENSION_1": "458",
"DIMENSION_2": "459",
rowId: 2,
},
{
"group0": "111",
"group1": "Ouput",
"group2": "1",
"METRIC": "test111",
"unit": "%",
"State": "test111-2221", // 父亲标识
"State1": "test111-2221", // 叶子结点标识
"DIMENSION_1": "458",
"DIMENSION_2": "459",
rowId: 3,
},
{
"group0": "111",
"group1": "Ouput",
"group2": "11.1",
"METRIC": "test1111",
"unit": "%",
"DIMENSION_1": null,
"DIMENSION_2": "459",
rowId: 4,
},
// 汇总行
{
"group0": "222",
"group1": "input",
"group2": "222-111",
"METRIC": "tes333",
"unit": "%",
// "State": "test111-2222",
"DIMENSION_1": "458",
"DIMENSION_2": "457.899",
rowId: 5,
},
{
"group0": "222",
"group1": "input",
"group2": "222-111",
"METRIC": "tes333",
"unit": "%",
"State": "test111-2222", // 非汇总行值
"DIMENSION_1": "458",
"DIMENSION_2": "459",
rowId: 6,
},
]
const option = {
// records: data.map((item,index)=>{
// item.rowindex = index
// return item
// }),
records: useData.map((item,index)=>{
item.rowindex = index
return item
}),
rowSeriesNumber: {
title: "行号",
width: 70,
format: (col, row, table)=> {
// 使用固定列叶子结点所在列，从1开始数, 可以拿到原数据
let record = table.getRecordByCell(6, row) || {}
let a = table.getCellRawValue(6,row) || []
// console.log('11111',col,row,record[0], a)
return record[0]?.rowId || row
}
},
// 根节点行，有多少值，就有多少项
rowTree: [
{
dimensionKey: 'group0',
value: '111',
},
{
dimensionKey: 'group0',
value: '222',
}
// {
// dimensionKey: 'group1',
// value: 'Ouput',
// },
// {
// dimensionKey: 'group1',
// value: 'input'
// },
],
columnTree: [
{
value: '趋势',
indicatorKey: 'DIMENSION_0',
dimensionKey:'DIMENSION_0'
},
{
value: '2024-12-01',
indicatorKey: 'DIMENSION_1',
dimensionKey:'DIMENSION_1'
},
{
value: '2024-12-02',
indicatorKey: 'DIMENSION_2',
dimensionKey:'DIMENSION_2'
}
],
// 行维度列（非数据列），配置扩展行时，只指定第一个列也可以
rows: [
{
dimensionKey: 'group0',
title: '分组0',
minWidth: 100
}
// {
// dimensionKey: 'group1',
// title: '分组1',
// minWidth: 100
// },
// {
// dimensionKey: 'group2',
// title: '分组2',
// minWidth: 100
// },
// {
// dimensionKey: 'metric',
// title: '树节点列',
// minWidth: 100
// },
// {
// dimensionKey: 'unit',
// title: '单位',
// minWidth: 100
// },
],
// columnTree:[],
// 无列维度
columns: [
// {
// dimensionKey: 'group0',
// title: '分组0',
// headerStyle: {
// textStick: true
// },
// minWidth: '100'
// },
// {
// dimensionKey: 'group1',
// title: '分组1',
// headerStyle: {
// textStick: true
// },
// minWidth: '100'
// },
// {
// dimensionKey: 'group2',
// title: '分组2',
// headerStyle: {
// textStick: true
// },
// minWidth: '100'
// },
// {
// dimensionKey: 'unit',
// title: '单位',
// headerStyle: {
// textStick: true
// },
// width: 'auto'
// }
],
extensionRows: [
{
rows: [{ dimensionKey: 'group1', title: '分组1', minWidth: 100 }],
rowTree(args) {
const valueData = ['Ouput','input']
// valueData.forEach((item)=>{
const currentROWS = useData.find((data)=>{
return data['group0'] === args[0].value
})
console.log('---11111111---2222----',args,currentROWS)

        return [{
          dimensionKey: 'group1',
          value: currentROWS['group1'] || 'input'
        }]
      },
    },
    {
      rows: [{ dimensionKey: 'group2', title: '分组2', minWidth: 100 }, ],
      rowTree(args) {
        console.log('分组2', args)
        if (args[1].value === 'input') {
          return [
            {
              dimensionKey: 'group2',
              value: '222-111'
            }
          ]
        }
        return [
            {
              dimensionKey: 'group2',
              value: '1'
            },
            {
              dimensionKey: 'group2',
              value: '11.1'
            },
        ]
      },
    },
    {
      rows: [{ dimensionKey: 'METRIC', title: '树节点列', minWidth: 200 }, 'State', 'State1'],
      rowTree(args) {
        console.log('args[1].value', args)
        if (args[2].value === '1') {
          return [
            {
              dimensionKey: 'METRIC',
              value: 'test111',
              children: [
                {
                  dimensionKey: 'State',
                  value: 'test111-2221',
                  children: [{
                    dimensionKey: 'State1',
                    value: 'test111-2221',
                  }]
                },
              ]
            },
          ]
        }
        if(args[2].value === '11.1'){
          return [
            {
              dimensionKey: 'METRIC',
              value: 'test1111'
            },
          ]
        }
        return [
            {
              dimensionKey: 'METRIC',
              value: 'tes333',
              children: [
                {
                  dimensionKey: 'State',
                  value: 'test111-2222'
                },
              ]
            },
        ]
      },
    },
    {
      rows: [{ dimensionKey: 'unit', title: "单位", minWidth: 200 }],
      rowTree(args) {
        // 前置列的下标
        if (args[3].value === 'test111') {
          console.log('args', args)
          return [
            {
              dimensionKey: 'unit',
              value: '个',
            },
          ]
        }
        return [
            {
              dimensionKey: 'unit',
              value: '%',
            },
        ]
      },
    }
  ],
  indicators: [
    {
      indicatorKey: 'DIMENSION_1',
      title: '2024-12-01',
      minWidth: 120,
      showSort: false,
      headerStyle: {
        fontWeight: 'normal'
      },
      // format: value => {
      //   if (value) {
      //     return '$' + Number(value).toFixed(2);
      //   }
      //   return '';
      // },
      style: {
        padding: [16, 28, 16, 28],
        color(args) {
          if (args.dataValue >= 0) {
            return 'black';
          }
          return 'red';
        }
      }
    },
    {
      indicatorKey: 'DIMENSION_2',
      title: '2024-12-02',
      minWidth: 120,
      showSort: false,
      headerStyle: {
        fontWeight: 'normal'
      },
      // format: value => {
      //   if (value) {
      //     return '$' + Number(value).toFixed(2);
      //   }
      //   return '';
      // },
      style: {
        padding: [16, 28, 16, 28],
        color(args) {
          if (args.dataValue >= 0) {
            return 'black';
          }
          return 'red';
        }
      }
    },
  ],
  corner: {
    titleOnDimension: 'row',
    headerStyle: {
      textStick: true
    }
  },
  rowHierarchyType: 'tree',
  widthMode: 'standard',
  rowHierarchyIndent: 20,
  rowExpandLevel: 1,
  rowHierarchyTextStartAlignment: true,
  dragHeaderMode: 'all'
};

const instance = new VTable.PivotTable(document.getElementById(CONTAINER_ID), option);
window.tableInstance = instance;
`

What does the proposed API look like?

类似单元格 stye 等，有特定的配置项即可

Start with the PivotTable option example in the issue, especially extensionRows, rowTree, custom headers, and cell-related configuration. Define the configuration needed to customize merged tree-table headers and cells, then verify that the proposed API supports the shown hierarchy and data before adding a focused demo or test; no repository file or test is named in the issue.