refactor(csv): remove runeCount() function

[timreichen]

• replaces runeCount() with length of strings

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.81%. Comparing base (73f236d) to head (12b53eb).

Files	Patch %	Lines
csv/_io.ts	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5298      +/-   ##
==========================================
- Coverage   95.81%   95.81%   -0.01%     
==========================================
  Files         457      457              
  Lines       37907    37895      -12     
  Branches     5568     5568              
==========================================
- Hits        36321    36309      -12     
  Misses       1546     1546              
  Partials       40       40              

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[kt3k]

This makes the count of characters broken for surrogate pair characters

> "🐱".length
2
> Array.from("🐱").length
1

[timreichen]

This makes the count of characters broken for surrogate pair characters

> "🐱".length
2
> Array.from("🐱").length
1

Ah damn, sorry for the oversight. I think we should add a test for that.