support StringViews 2.0

[stevengj]

Updates the package to use StringViews 2.0 if available (which has minor breaking changes with 1.0 that shouldn't affect this package). In Julia 1.14, where the StringView type is merged into Base, the StringViews 2.0 package becomes a simple stub around the Base type.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.37%. Comparing base (3712291) to head (703f3c7).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #599      +/-   ##
==========================================
- Coverage   87.43%   87.37%   -0.07%     
==========================================
  Files          26       27       +1     
  Lines        3288     3383      +95     
==========================================
+ Hits         2875     2956      +81     
- Misses        413      427      +14     

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