fix(Select): retain selected options during remote searches

[RylanBot]

🤔 这个 PR 的性质是？

• 日常 bug 修复
• 新特性提交
• 文档改进
• 演示代码改进
• 组件样式/交互改进
• CI/CD 改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他

🔗 相关 Issue

• [Select] filterable+multiple+onSearch远程搜索，不在options的选中值展示不出来 #3923

💡 需求背景和解决方案

📝 更新日志

• fix(Select): 修复在选中选项后，输入框被清空但未触发对应的 onSearch 回调问题

• fix(Select): 修复开启 onSearch 与 multiple 时，选中选项丢失的问题

• 本条 PR 不需要纳入 Changelog

☑️ 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
• Changelog 已提供或无须提供

[pkg-pr-new]

tdesign-react-demo

npm i https://pkg.pr.new/tdesign-react@3926

commit: 27d6653

[github-actions]

[Copilot]

Pull Request Overview

This PR enhances the Select component's remote search functionality by preserving selected options in the value-to-option mapping and triggering initial search on dropdown open. The changes enable the Select component to properly handle remote search scenarios where options are dynamically fetched.

• Preserves selected options in mapping to prevent state loss during remote searches
• Triggers search on dropdown open when search handler exists and input is empty
• Updates remote-search example to demonstrate both single and multiple select modes with loading states

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/components/select/hooks/useOptions.ts	Adds logic to merge previous selected options into the value-to-option mapping and exports helper function for value selection checking
packages/components/select/base/Select.tsx	Calls onSearch with empty string when dropdown opens for remote search initialization
packages/components/select/_example/remote-search.tsx	Rewrites example to showcase both single and multiple select with proper remote search implementation
test/snap/snapshots/ssr.test.jsx.snap	Updates SSR snapshot to reflect new example structure with Space component
test/snap/snapshots/csr.test.jsx.snap	Updates CSR snapshot to reflect new example structure with loading states

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