fix(select): 修复多选模式下key可能为undefined的场景

[Carryours]

场景

Select组件为多选模式下，options从远程加载时。如果初始值中包含未加载到的option选项，会导致key值为undefined。
OverFlow组件在渲染标签Item时，如果没有key值会使用index作为key，并且当option的value值为number类型，则会导致key值重复并且删除Selected值会出现问题。

关联代码

 // ================================= Item =================================
  const getKey = (item: any, index: number) => {
    if (typeof props.itemKey === 'function') {
      return props.itemKey(item);
    }
    return (props.itemKey && (item as any)?.[props.itemKey]) ?? index;
  };

复现场景

https://codesandbox.io/p/sandbox/elastic-river-ng9wcp?file=%2Fsrc%2FApp.vue%3A10%2C31

修复后

2025-02-14.14.54.56.mov

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