Add benchmarks for extended year / ParsedDateTime API

[sylvestre]

Cover the extended year functionality introduced in #263:

• Basic extended year parsing (year 10000)
• Rollover from in-range to extended (9999-12-31 +1 day)
• Relative parsing with extended year base date
• Large year parsing (year 999999)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.29%. Comparing base (30ea391) to head (34481be).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #276   +/-   ##
=======================================
  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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