Add CodSpeed benchmark integration

[codspeed-hq]

Summary

• Added performance benchmarks using pytest-codspeed (v4.3.0) covering core framework operations: application creation, simple and parametrized GET requests, POST requests with Pydantic model validation, and route resolution across multiple registered routes.
• Added a GitHub Actions workflow (.github/workflows/codspeed.yml) that runs benchmarks on every push to main, on pull requests, and on manual dispatch. Uses OIDC authentication and simulation mode.
• Added the CodSpeed badge to the README.

What's being measured

Benchmark	Description
test_bench_app_creation	Cost of instantiating a Ravyn app with multiple routes
test_bench_simple_get_request	Full request/response cycle for a plain GET endpoint
test_bench_parametrized_get_request	GET request with path parameter extraction
test_bench_post_request_with_validation	POST request with Pydantic body validation
test_bench_multiple_routes	Route resolution when several routes are registered

Next steps

• Merge this PR to start collecting baseline performance data on main.
• Consider adding more granular benchmarks as the framework evolves (middleware chains, dependency injection, serialization, etc.).
• Visit the CodSpeed dashboard to view results once the first run completes.

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 5 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

• test_bench_simple_get_request: 4.5 ms
• test_bench_multiple_routes: 5.6 ms
• test_bench_parametrized_get_request: 4.6 ms
• test_bench_post_request_with_validation: 4.6 ms
• test_bench_app_creation: 2.6 ms

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