Add real-world examples and performance benchmarks

[abhiasmt]

Summary

This PR improves developer experience by adding:

• Real-world usage examples (chat UI, virtualization, responsive layout)
• Best practices for using prepare() and layout()
• Performance comparison with DOM-based approaches
• React integration example
• Simple benchmark script

Motivation

While Pretext is powerful, new users may struggle to understand:

• When to use prepare() vs layout()
• How it fits into real-world applications
• Its performance benefits compared to DOM measurement

This PR aims to bridge that gap and improve adoption.

Changes

• Updated README.md with new sections:
  • Real-world use cases
  • Best practices
  • Performance comparison
  • React example
• Added /benchmarks/simple-benchmark.ts

Impact

• Improves onboarding for new developers
• Makes performance benefits clearer
• Encourages correct usage patterns

Let me know if you'd like me to expand examples (Vue, Canvas, etc.)