Add CodSpeed for continuous performance monitoring

[codspeed-hq]

Summary

This PR sets up CodSpeed for continuous performance monitoring in CI, enabling automated detection of performance regressions.

Changes

• Dependencies: Downgraded vitest from v4 to v3 and added @codspeed/vitest-plugin@5.0.1
  • Note: vitest v4 is not yet supported by CodSpeed (tracking issue: Support vitest v4 CodSpeedHQ/codspeed-node#67)
• Configuration: Updated vitest.config.ts to include the CodSpeed plugin
• Benchmarks: Created benchmark files for core functionality:
  • benchmarks/schema-builder.bench.ts - GraphQL schema parsing, building, and merging operations
  • benchmarks/directive-parser.bench.ts - Directive parsing and schema generation
• CI/CD: Added .github/workflows/codspeed.yml with OIDC authentication
• Documentation: Added CodSpeed badge to README

Version Note

This PR includes a downgrade from vitest v4 to v3 because CodSpeed's vitest plugin does not yet support v4. Once v4 support is added (see tracking issue above), we can upgrade back to v4.

Test Plan

• Benchmarks run successfully locally with pnpm bench
• CodSpeed workflow runs successfully in CI
• Performance data is collected and reported on CodSpeed dashboard

Next Steps

Once this PR is merged:

1. Monitor the CodSpeed workflow to ensure it completes successfully
2. Review initial performance baselines on the CodSpeed dashboard
3. Set up performance regression checks on future PRs

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	75.33%	2477 / 3288
🔵	Statements	75.33%	2477 / 3288
🔵	Functions	76.3%	132 / 173
🔵	Branches	80.35%	589 / 733

File Coverage

No changed files found.

Generated in workflow #326 for commit a47f30d by the Vitest Coverage Report Action

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 8 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

• parse multiple directives: 1.2 ms
• parse complex schema: 1.2 ms
• generate directive schema: 73.1 µs
• parse single directive: 450.9 µs
• build complex schema: 3.3 ms
• parse simple schema: 370.6 µs
• merge multiple schemas: 2.8 ms
• build simple schema: 2.4 ms

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