chore(cascader): demo拆解与规范

[Alex-huxiyang]

🤔 这个变动的性质是？

• 演示代码改进

🔗 相关 Issue

💡 需求背景和解决方案

☑️ 请求合并前的自查清单

⚠️ 请自检并全部勾选全部选项。⚠️

• 文档已补充或无须补充
• 代码演示已提供或无须提供
• TypeScript 定义已补充或无须补充
• fork仓库代码是否为最新避免文件冲突
• Files changed 没有 package.json lock 等无关文件

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.21%. Comparing base (0f303f0) to head (aafb89c).

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #2144   +/-   ##
=======================================
  Coverage   86.21%   86.21%           
=======================================
  Files         215      215           
  Lines       22814    22814           
  Branches     2501     2501           
=======================================
  Hits        19669    19669           
  Misses       3140     3140           
  Partials        5        5           

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