Add CodSpeed performance benchmarks and CI integration

[codspeed-hq]

Summary

This PR sets up continuous performance measurement for kee using CodSpeed. It adds a criterion-based benchmark suite covering the library's hot paths and a GitHub Actions workflow that runs the benchmarks on every push and pull request.

Changes

• benches/kee_benchmarks.rs: A new benchmark suite exercising the public library API:
  • ProfileInfo JSON serialization and deserialization
  • KeeConfig construction across multiple sizes (10 / 100 / 1000 profiles)
  • Profile lookup (get_profile) and listing (list_profiles)
  • Full KeeConfig serialization / deserialization round-trips at varying sizes
  • Profile removal
• Cargo.toml: Registered the kee_benchmarks bench target (harness = false) and added the codspeed-criterion-compat dev-dependency (aliased as criterion). This is a drop-in replacement for criterion that adds CodSpeed instrumentation while keeping the standard criterion API.
• .github/workflows/codspeed.yml: A workflow that builds the benchmarks with cargo codspeed build and runs them via the CodSpeed action in simulation mode, authenticated through OpenID Connect (no token required).
• README.md: Added the CodSpeed badge.

Notes

• The benchmarks run in simulation mode, CodSpeed's deterministic CPU instrument, which provides low-variance measurements on standard ubuntu-latest runners. Macro runners are not required for this mode.
• All benchmarks were validated locally before opening this PR.

Next steps

• Merge this PR so CodSpeed can establish a performance baseline from the main branch.
• Subsequent pull requests will automatically receive performance reports comparing against that baseline.
• Consider expanding coverage to the AWS config parsing paths (AwsManager) if those are exposed for benchmarking in the future.

[codecov]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 14 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

• config_build[10]: 31.6 µs
• config_build[100]: 251 µs
• config_build[1000]: 2.5 ms
• config_get_profile: 1.2 µs
• config_list_profiles: 19.3 µs
• config_remove_profile: 56.6 µs
• deserialize[10]: 42.2 µs
• deserialize[100]: 334.6 µs
• deserialize[1000]: 3.3 ms
• serialize[10]: 24.4 µs
• serialize[100]: 176.5 µs
• serialize[1000]: 1.8 ms
• profile_info_deserialize: 6.8 µs
• profile_info_serialize: 5.6 µs

---