Add CodSpeed for continuous performance benchmarking

[codspeed-hq]

Summary

This PR integrates CodSpeed to enable continuous performance benchmarking in CI. CodSpeed will automatically track performance changes on every commit and pull request, providing detailed insights and catching performance regressions early.

Changes Made

• Downgraded vitest from v4 to v3.2.4: CodSpeed currently supports vitest v3, not v4. This downgrade is necessary for compatibility with the CodSpeed vitest plugin. See tracking issue: Support vitest v4 CodSpeedHQ/codspeed-node#67
• Added @codspeed/vitest-plugin v5.0.1: Integrated the official CodSpeed plugin for vitest benchmarks
• Updated vitest.config.ts: Configured the CodSpeed plugin to instrument benchmarks
• Created .github/workflows/codspeed.yml: New GitHub Actions workflow that runs benchmarks on every push to main, pull requests, and manual triggers using OIDC authentication
• Added CodSpeed badge to README: Shows benchmark status and links to the CodSpeed dashboard

How It Works

The CodSpeed workflow will:

1. Run on every push to main and on all pull requests
2. Execute the existing benchmarks in the bench package
3. Upload results to CodSpeed for analysis
4. Provide performance comparison reports on PRs showing any performance changes

Testing

Benchmarks have been tested locally and run successfully with the new configuration:

• All existing benchmarks pass
• CodSpeed plugin correctly instruments the benchmark runs

Next Steps

After merging, the first workflow run will establish baseline performance metrics. Subsequent runs will compare against this baseline to detect performance changes.

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View logs

[codspeed-hq]

CodSpeed Performance Report

Congrats! CodSpeed is installed 🎉

🆕 6 new benchmarks were detected.

You will start to see performance impacts in the reports once the benchmarks are run from your default branch.

Detected benchmarks

• marked: 13.1 ms
• commonmark: 13.9 ms
• markdown-exit-commonmark: 22 ms
• markdown-it-commonmark: 23.6 ms
• markdown-exit: 28 ms
• markdown-it: 29.5 ms