Changing ErrMode::Cut to ErrMode::Backtrack to allow alt parser flow (Fix for uutils/coreutils issue 8754)

[stillbeingnick]

This PR purposes changes that fix uutils/coreutils#8754 after a chore in coreutils to move from parse_datetime v0.11.0 to the latest including this fix.

Summary:

• Replaced ErrMode::Cut(e) with ErrMode::BackTrack(e) within date items parser functions to enable alternate parser flow to continue instead of failing prematurely.

Details:

• When using ErrMode::Cut(e) within a parser it signals that the error is not recoverable and the parser chain unwinds and fails. In some cases this is desirable but for the parser functions in date it seems they are recoverable errors.
  • https://docs.rs/winnow/0.7.13/winnow/error/enum.ErrMode.html#variant.Backtrack
  • https://docs.rs/winnow/0.7.13/winnow/error/enum.ErrMode.html#variant.Cut

Testing notes:

• New tests have been added to confirm parsing of relative time up to 12 whole decimal places and inverse test cases testing for failure of 13 -> 15 whole decimal places.
• All previous test cases remain unchanged.

[cakebaker]

Can you please run cargo fmt and cargo clippy? Thanks.

[stillbeingnick]

@cakebaker All fixed up!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (29e3686) to head (3074fe3).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #238   +/-   ##
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[cakebaker]

Thanks for your PR!