Using AI Assistant to identity (and fix) performance bottlenecks

[whomwah]

This pull request introduces a comprehensive benchmarking suite for the RQRCode library, enabling developers to measure and track performance and memory usage across different QR code export formats. It also updates documentation and tooling to support these new benchmarks and clarifies Ruby version requirements.

Performance Improvements

• SVG rendering: Improved by +130% (from 184 i/s to 424 i/s) with 71% memory reduction
• HTML rendering: Now the fastest export format at 1,876 i/s (rendering-only benchmark)
• End-to-end performance: All formats now perform similarly (~32-34 i/s for medium QR codes) - SVG optimizations closed the gap with other formats
• Memory efficiency: HTML now uses 6x less memory than SVG (previously 22x), with HTML at 18.0 MB vs SVG at 113.8 MB

Key Benchmark Insights

• End-to-end benchmarks show that QR generation dominates performance, with all export formats achieving similar speeds
• Rendering-only benchmarks reveal significant improvements in export efficiency, particularly for SVG and HTML
• HTML is the most memory-efficient format (451 objects allocated vs 2,157,951 for SVG)
• SVG improvements reduced the performance gap vs HTML from 10x to 4.4x

Benchmarking Infrastructure and Usage

• Added a full benchmark suite in the benchmark/ directory, including scripts for SVG, PNG, HTML, ANSI, and format comparison, as well as a detailed benchmark/README.md explaining usage, metrics, and interpretation of results. Benchmark results are saved as JSON for tracking over time.
• Introduced benchmark_helper.rb to provide shared benchmarking utilities, including methods for running IPS (iterations/sec), memory, and stack profiling, and saving results.
• Added Rake tasks for running benchmarks individually or all at once, integrating them into the development workflow.

Documentation and Developer Experience

• Added AGENTS.md as a development guide for AI agents, summarizing build/test/lint commands, code style, file structure, dependencies, and commit message conventions.
• Updated README.md to reflect the new minimum Ruby version (>= 3.2.0), document benchmark usage, and clarify contribution guidelines.

Tooling and Configuration

• Updated the Ruby matrix in the GitHub workflow to test only supported versions (3.2, 3.3, 3.4, 4.0).
• Added a commented-out reference to rqrcode_core in the Gemfile for easier local development.