test: add unit tests for usePrevious hook

[broBinChen]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• TypeScript definition update
• Bundle size optimization
• Performance optimization
• Enhancement feature
• Internationalization
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

N/A - This is a proactive improvement to increase test coverage for the usePrevious hook.

💡 Background and solution

Problem:
The usePrevious hook was missing unit tests, which could lead to potential regressions and makes it harder to maintain code quality and reliability.

Solution:
Added comprehensive unit tests for the usePrevious hook with 15 test cases covering:

1. Basic functionality: Hook definition, initial values, readonly behavior
2. State tracking: Previous value tracking for primitives, strings, objects, and computed refs
3. Custom shouldUpdate function: Custom update logic, undefined handling, conditional updates
4. Default shouldUpdate behavior: Object.is comparison, NaN handling
5. Edge cases: Rapid state changes, boolean values, null/undefined values

All tests pass successfully, ensuring the hook works correctly across various scenarios and edge cases.

📝 Changelog

Language	Changelog
🇺🇸 English	Internal improvement: Added comprehensive unit tests for usePrevious hook (no user-facing changes)
🇨🇳 Chinese	内部改进：为 usePrevious hook 添加了全面的单元测试（无用户侧变化）

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Follow our Code of Conduct
• Read the Contributing Guidelines
• Read the docs
• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

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