Update benchmark README with latest performance data and add interactive HTML visualization

[Copilot]

This PR updates the benchmark documentation with fresh performance data and adds an interactive HTML visualization for better analysis of the JSON5 performance comparison.

Changes Made

📊 Updated benchmark/README.md

• Refreshed performance data table with latest benchmark results from benchmark_results_2025-06-25_01-31-43.csv
• Updated overall performance comparison statistics:
  • JSON is 4.45× faster than JSON5 (previously 3.90×)
  • JSON is 2.51× faster than External-JSON5 (previously 2.75×)
  • External-JSON5 is 1.77× faster than JSON5 (previously 1.42×)
• Added documentation for the new HTML visualization file
• Updated example output snippets with current timing data

🎯 Created benchmark_visualization.html

• Self-contained HTML file using Chart.js (widely known charting library as requested)
• Interactive visualization with multiple chart types:
  • Performance by data type and operation - Bar chart showing detailed comparison across all test cases
  • Serialization vs deserialization - Bar chart comparing average performance by operation type
  • Overall performance comparison - Doughnut chart showing relative performance distribution
  • Performance ratios - Bar chart displaying "times slower" multipliers
• Responsive design with modern styling
• Embedded actual benchmark data from the latest CSV results
• Can be opened directly in any web browser

Key Performance Insights

The latest benchmark data shows consistent performance patterns:

• JSON (kotlinx.serialization) remains the performance leader across all scenarios
• External-JSON5 provides good JSON5 features with reasonable performance
• JSON5 (this project) offers seamless kotlinx.serialization integration but at a performance cost

Testing

• ✅ All existing tests pass (./gradlew :benchmark:test)
• ✅ Build succeeds (./gradlew :benchmark:build)
• ✅ HTML file is valid and contains expected 4 interactive charts
• ✅ Documentation is consistent and up-to-date

The interactive visualization makes it easy to analyze performance trends and understand the trade-offs between the three JSON libraries.

Fixes #56.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[hossain-khan]