Update package manager from pnpm to bun

[akemmanuel]

This PR updates the package manager from pnpm to bun, which offers several benefits:

🚀 Performance Improvements:

• Up to 2x faster dependency installation
• Significantly faster package resolution
• Reduced disk space usage

🛠️ Developer Experience:

• Single binary installation (no separate CLI)
• Built-in test runner and bundler
• Better TypeScript support out of the box

📦 Migration Benefits:

• Compatible with existing package.json files
• Same command structure (bun install, bun run build, etc.)
• Zero configuration needed

The changes replace all pnpm references with bun equivalents in the README.md file while maintaining the same functionality. This migration will improve development speed and reduce setup complexity for new contributors.