Add CodSpeed continuous performance tracking

[codspeed-hq]

Summary

• Added pytest-codspeed (v4.3.0+) as a testing dependency to enable performance benchmarking with CodSpeed's CPU simulation instrument.
• Created a benchmark suite in tests/benchmarks/test_benchmarks.py with 10 benchmarks covering:
  • Encoder performance: JSON serialization/deserialization of dataclasses, lists, and structure molding via apply_structure
  • Command registration: Measuring overhead of registering simple and complex (multi-option) commands
  • Command invocation: End-to-end invocation of commands with positional arguments, options, and JSON parameter deserialization
  • Group operations: Group creation and command attachment
• Added a GitHub Actions workflow (.github/workflows/codspeed.yml) that runs benchmarks on pushes to main, pull requests, and manual dispatches, using OIDC authentication and simulation mode.
• Added the CodSpeed badge to the README.

Next steps

• Merge this PR to establish the performance baseline on main.
• Future PRs will automatically receive performance reports comparing against that baseline.
• Consider adding more benchmarks as the project evolves (e.g., middleware chains, async commands, state management).

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 10 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_json_encode_list: 191.5 µs
• test_bench_invoke_json_command: 698.8 µs
• test_bench_group_creation_and_command: 260 µs
• test_bench_command_registration_with_options: 523 µs
• test_bench_invoke_simple_command: 710.8 µs
• test_bench_command_registration: 330.9 µs
• test_bench_apply_structure_list: 166.1 µs
• test_bench_json_encode_dataclass: 197.9 µs
• test_bench_invoke_command_with_options: 796.8 µs
• test_bench_apply_structure_dataclass: 138.8 µs

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