Add CodSpeed performance benchmarks

[codspeed-hq]

Summary

• Added 18 performance benchmarks covering the core components of asyncz:
  • Utility functions: to_timezone, to_datetime, datetime_to_utc_timestamp, utc_timestamp_to_datetime, timedelta_seconds, datetime_ceil, ref_to_obj, check_callable_args
  • Trigger creation: CronTrigger, CronTrigger.from_crontab, IntervalTrigger, DateTrigger
  • Trigger computation: next fire time calculations for cron (with and without previous time), crontab expressions, interval (with and without previous time), and date triggers
• Added a GitHub Actions workflow (.github/workflows/codspeed.yml) that runs benchmarks on push to main and on pull requests, using OIDC authentication and simulation mode
• Added the CodSpeed badge to the README

Next Steps

• Visit the CodSpeed dashboard to view benchmark results after the first CI run
• Add more benchmarks as new features are developed, especially around scheduler operations and store serialization
• Consider adding benchmarks for async operations once the scheduler benchmarking patterns are established

Test Plan

• Verify the CodSpeed workflow runs successfully in CI
• Check that all 18 benchmarks are reported on the CodSpeed dashboard
• Confirm the CodSpeed badge renders correctly in the README

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 18 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_interval_trigger_next_fire_time_with_previous: 277 µs
• test_utc_timestamp_to_datetime: 129.2 µs
• test_to_datetime_from_string: 199.6 µs
• test_create_date_trigger: 208 µs
• test_interval_trigger_next_fire_time: 283.6 µs
• test_create_cron_trigger_from_crontab: 853.6 µs
• test_check_callable_args: 212 µs
• test_crontab_trigger_next_fire_time: 1.1 ms
• test_ref_to_obj: 152.1 µs
• test_cron_trigger_next_fire_time: 1 ms
• test_datetime_to_utc_timestamp: 136 µs
• test_to_timezone_from_string: 135.8 µs
• test_create_interval_trigger: 252.8 µs
• test_cron_trigger_next_fire_time_with_previous: 1.2 ms
• test_date_trigger_next_fire_time: 165 µs
• test_datetime_ceil: 139.6 µs
• test_timedelta_seconds: 139.4 µs
• test_create_cron_trigger: 813 µs

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