fix: silently ignore unrecognized trailing alphabetic tokens after pure numbers

[0xSoftBoi]

Summary

• GNU date accepts inputs like 8j and 8 j, treating the leading number as an hour and silently discarding the unrecognized trailing word-token. parse_datetime currently rejects these with InvalidInput.
• This PR matches GNU behavior for these cases while keeping all existing error paths intact.

Implementation

• Added Item::Noise variant for unrecognized alphabetic tokens.
• Added noise_token() as the last alternative in parse_item(), so it only fires after every other parser has already failed.
• In DateTimeBuilder::try_from, a Noise item is accepted only when it directly follows a Pure number item (prev_was_pure guard). This ensures 8j and 8 j succeed while bogus +1 day, 2025-01-01 abcdef, and NotADate still return errors.
• Added noise_after_pure_number regression test.

Test Plan

• All 134+ existing tests pass
• New regression test covers both fixed inputs and error cases

Fixes #279

[codspeed-hq]

Merging this PR will degrade performance by 13.27%

❌ 2 regressed benchmarks
✅ 19 untouched benchmarks

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

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	parse_invalid_input	27.2 µs	31.4 µs	-13.27%
❌	parse_weekday	30 µs	31.5 µs	-4.83%

---

_{Comparing 0xSoftBoi:fix/ignore-trailing-noise-tokens (118bb5a) 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 (118bb5a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #286      +/-   ##
==========================================
+ Coverage   99.30%   99.31%   +0.01%     
==========================================
  Files          20       21       +1     
  Lines        3894     3953      +59     
  Branches      122      123       +1     
==========================================
+ Hits         3867     3926      +59     
  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	14.09% <20.89%> (+0.04%)	⬆️

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[sylvestre]

please run cargo fmt

[tomagsx]

Review bump on this PR. I see the current blockers are the formatting failure and the CodSpeed regression flag; I can follow up on the formatting immediately, but I’d still appreciate a maintainer read on whether the GNU-compat behavior for trailing noise-after-pure-number is acceptable before this drifts.