ice-appear支持预加载

### Summary | 概述

在appear-polyfill中做了预加载功能，针对图片可以做到比懒加载体验更好（没有白屏）

### Motivation | 背景

需要针对长列表做性能优化，但不希望图片懒加载影响到用户使用体验

### Usage example | 使用示例

import VisibilityChange from '@ice/appear';

export default function Home() {
return (
{
console.log('Something has been shown.')
}}
onPreappear={() => {
console.log('Something has disappeard.')
}}
onDisappear={() => {
console.log('Something has disappeard.')
}}
>
Anything you want to show.

);
}

### Detailed design | 方案设计

1. 支持配置 intersectionObserver 的 api
2. 如果开发者配置了 preLoad 参数，则额外新建一个 observer 实例，收集 pre-appear 事件传入的函数，按需触发

### Additional context | 额外信息

_No response_

Start with the appear-polyfill implementation exposed as @ice/appear and inspect the VisibilityChange component's existing IntersectionObserver configuration and appear/disappear callbacks. Trace how the proposed preLoad option should create a separate observer and invoke onPreappear for the usage example, then verify the documented callback behavior.

Written by the indexing model from the issue text.