fix(isUppercase): assume characters lowercase by default

[pi0]

🔗 Linked issue

Resolves #69

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

isUppercase is used to return true for nonalphabetic characters such as -. This issue was not visible for the splitByCase util without custom splitters.

The fix checkes if string could be lowecased, it is an uppercase. (also adds tiny perf because the frequency of passed lowercase strings is much higher and it saves v8 engine to do anything for most of toLowercase() calls

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d2c281f) 100.00% compared to head (74ba20d) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #71   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            2         2           
  Lines          340       340           
  Branches        39        39           
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  Hits           340       340           

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