Add CodSpeed performance benchmarks

[codspeed-hq]

Summary

This PR integrates CodSpeed for continuous performance monitoring of the parse_datetime crate.

Changes

• Benchmark suite (benches/parse_datetime.rs): 17 benchmarks using codspeed-criterion-compat covering all major parsing paths:

  • ISO 8601 datetime (with and without T separator)
  • Date-only formats (ISO and slash notation)
  • Epoch timestamps (@...)
  • Relative time expressions (+3 days, 1 year 3 months 2 days ago)
  • Keyword-based parsing (yesterday, tomorrow, now)
  • Weekday parsing
  • Timezone offsets and named timezones
  • ctime format (Wed Jan 1 00:00:00 1997)
  • Datetime with delta (1997-01-01 00:00:00 +0000 +1 year)
  • Invalid input (error path)

• CI workflow (.github/workflows/codspeed.yml): Runs benchmarks on push to main, on pull requests, and on workflow_dispatch using CodSpeed's simulation mode for reproducible, hardware-independent measurements.

• Cargo.toml: Added codspeed-criterion-compat as a dev-dependency and registered the benchmark target.

• README.md: Added CodSpeed badge.

Next steps

Once merged, CodSpeed will automatically run benchmarks on every PR and report any performance regressions or improvements directly in the PR checks. You can view detailed results and flame graphs on the CodSpeed dashboard.

[codspeed-hq]

Congrats! CodSpeed is installed 🎉

🆕 17 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

• parse_weekday: 31.2 µs
• parse_ctime_format: 66.2 µs
• parse_datetime_with_tz_name: 59.8 µs
• parse_tomorrow: 21.2 µs
• parse_datetime_with_delta: 47.8 µs
• parse_datetime_ending_in_z: 58.5 µs
• parse_timezone_offset: 45 µs
• parse_relative_time: 26.6 µs
• parse_date_only: 19 µs
• parse_date_slash_format: 18.8 µs
• parse_now: 20.7 µs
• parse_relative_time_complex: 66.5 µs
• parse_yesterday: 21.7 µs
• parse_invalid_input: 27.3 µs
• parse_epoch_timestamp: 7.5 µs
• parse_iso_datetime: 34.9 µs
• parse_iso_datetime_t_separator: 34.1 µs

---

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.29%. Comparing base (ee4971c) to head (70a08a8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #273   +/-   ##
=======================================
  Coverage   99.29%   99.29%           
=======================================
  Files          20       20           
  Lines        3847     3847           
  Branches      121      121           
=======================================
  Hits         3820     3820           
  Misses         26       26           
  Partials        1        1           

Flag	Coverage Δ
macos_latest	99.29% <ø> (ø)
ubuntu_latest	99.29% <ø> (ø)
windows_latest	14.21% <ø> (ø)

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