fix: support HH:MM am/pm time formats in combined date-time parsing

[0xSoftBoi]

Summary

• The combined date-time parser (combined::parse) used time::iso which only accepts 24-hour notation, causing inputs like "2024-06-15 12:00 PM" to fail — the ISO parser greedily consumed "12:00" and left "pm" orphaned
• Switched to time::parse (which tries am_pm_time first with fallback to iso), so am/pm suffixes are now correctly consumed as part of the time
• Case insensitivity is already handled by parse_items lowercasing input before parsing

Fixes #282

Test plan

• Added test date_and_time_ampm covering all three failing inputs from the issue: "2024-06-15 12:00 PM", "2024-06-15 11:30am", "2024-06-15 3:00 PM"
• All 376 existing tests pass (cargo test)
• No regressions — am_pm_time fails gracefully (backtrack) on inputs without meridiem, falling through to iso

[codspeed-hq]

Merging this PR will degrade performance by 3.93%

❌ 2 regressed benchmarks
✅ 19 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	parse_weekday	30 µs	31.2 µs	-3.93%
❌	parse_extended_year_relative	30.9 µs	32.2 µs	-3.89%

---

_{Comparing 0xSoftBoi:fix/hhmm-ampm-parsing (fdef5ec) with main (7440dd9)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.31%. Comparing base (7440dd9) to head (fdef5ec).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #284   +/-   ##
=======================================
  Coverage   99.30%   99.31%           
=======================================
  Files          20       20           
  Lines        3894     3941   +47     
  Branches      122      127    +5     
=======================================
+ Hits         3867     3914   +47     
  Misses         26       26           
  Partials        1        1           

Flag	Coverage Δ
macos_latest	99.31% <100.00%> (+<0.01%)	⬆️
ubuntu_latest	99.31% <100.00%> (+<0.01%)	⬆️
windows_latest	14.26% <34.69%> (+0.21%)	⬆️

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[sylvestre]

i am surprised to see potential perf regression here. what is your take here?

[tomagsx]

Review bump on this one. Functional coverage looks good and CI is green aside from the CodSpeed regression flag. The remaining question seems to be whether the measured perf hit is acceptable for the am/pm fix, so I’d really appreciate a maintainer take on that tradeoff when you have a chance.