Add CodSpeed performance benchmarking integration

[codspeed-hq]

Summary

This PR integrates CodSpeed continuous performance testing into the python-cqrs project to enable automated performance monitoring in CI.

Changes Made

Dependencies

• Added pytest-codspeed==4.2.0 to dev dependencies in pyproject.toml

Benchmarks

Created a new benchmarks/ directory with comprehensive benchmark suites covering:

• Request Handling (test_benchmark_request_handling.py): Benchmarks for command and query handling, including batch operations
• Event Handling (test_benchmark_event_handling.py): Benchmarks for event processing and notification event creation
• Serialization (test_benchmark_serialization.py): Benchmarks for request/response serialization and complex nested structures

CI Integration

• Added .github/workflows/codspeed.yml workflow that:
  • Runs on pushes to main/master and all pull requests
  • Uses CodSpeed action v4 with simulation mode
  • Uses OIDC authentication for secure runs
  • Runs benchmarks with pytest benchmarks/ --codspeed

Documentation

• Added CodSpeed badge to README.md linking to the project's CodSpeed dashboard

Next Steps

Once this PR is merged:

1. The CodSpeed workflow will run and establish baseline performance metrics
2. Future PRs will automatically receive performance comparison reports
3. Performance regressions will be visible directly in PR reviews

Testing

The benchmarks are designed to measure real-world performance characteristics of the CQRS framework components including mediator operations, event handling, and data serialization.

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 11 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_benchmark_request_to_dict: 69.7 µs
• test_benchmark_response_to_dict: 57.3 µs
• test_benchmark_request_from_dict: 29.4 µs
• test_benchmark_command_handling: 15.8 µs
• test_benchmark_complex_nested_structure: 58.3 µs
• test_benchmark_response_from_dict: 28.3 µs
• test_benchmark_event_processing: 24.6 µs
• test_benchmark_multiple_commands: 15.9 µs
• test_benchmark_notification_event: 118.1 µs
• test_benchmark_query_handling: 16.3 µs
• test_benchmark_multiple_events: 17.5 µs

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