Update Chinese translations to match latest English versions

[mk965]

Summary

This PR updates all Chinese documentation files to fully align with their English counterparts, ensuring Chinese users have access to the most current and accurate information.

Changes Made

📄 README_zh-CN.md

• Updated code examples to use modern ES6 import syntax (import {Tween, Easing})
• Reorganized installation section with methods ranked by preference
• Added comprehensive installation instructions (npm, CDN, manual build, etc.)
• Updated feature descriptions to match English version exactly
• Added "People" section with maintainer information

📋 docs/contributor_guide_zh-CN.md

• Complete rewrite to match English version structure and content
• Updated toolchain descriptions (Prettier + ESLint replacing outdated JSCS + JSHint)
• Fixed all section titles and content organization
• Updated testing processes and CI/CD information

📖 docs/user_guide_zh-CN.md

• Complete retranslation with all latest content included
• Updated all API examples to use modern syntax
• Added documentation for new features: pause, Group, dynamic, setNow, etc.
• Included performance optimization and best practices sections
• Updated callback functions and state management detailed explanations
• Added complete documentation for advanced tweening features

Verification

All translations have been carefully cross-referenced with the English versions to ensure:

• Accuracy of technical terminology
• Completeness of feature coverage
• Consistency in code examples
• Proper formatting and structure

The Chinese documentation now provides the same comprehensive information as the English version, making tween.js fully accessible to Chinese-speaking developers.