fix: accept vertical tab and form feed as whitespace between tokens

[wtcpython]

GNU date accepts \v and \f as whitespace between items, but winnow's multispace0/multispace1 do not, so inputs like Jan 23\v 2026 1:00AM are rejected (uutils/coreutils#13864). Replace them with local parsers covering the full ASCII whitespace set.

[codspeed-hq]

Merging this PR will degrade performance by 3.24%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 3 regressed benchmarks
✅ 18 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	parse_extended_large_year	36.4 µs	37.6 µs	-3.32%
❌	parse_date_only	37.9 µs	39.1 µs	-3.19%
❌	parse_extended_year	36.3 µs	37.5 µs	-3.19%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing wtcpython:accept-vertical-tab-whitespace (a965856) with main (4cf4db3)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.33%. Comparing base (4cf4db3) to head (a965856).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #322   +/-   ##
=======================================
  Coverage   99.33%   99.33%           
=======================================
  Files          21       21           
  Lines        4061     4075   +14     
  Branches      129      129           
=======================================
+ Hits         4034     4048   +14     
  Misses         26       26           
  Partials        1        1           

Flag	Coverage Δ
macos_latest	99.33% <100.00%> (+<0.01%)	⬆️
ubuntu_latest	99.33% <100.00%> (+<0.01%)	⬆️
windows_latest	13.91% <35.71%> (+0.07%)	⬆️

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[sylvestre]

The perf regression are acceptable