Add char extensions: Repeat and AsString

[Copilot]

Ports the char extension methods from CliFx's StringExtensions into PowerKit.

Changes

• PowerKit/Extensions/CharExtensions.cs — new file with two extension(char c) members:
  • Repeat(int count) → new string(c, count)
  • AsString() → c.Repeat(1)
• PowerKit.Tests/CharExtensionsTests.cs — unit tests for both methods

Usage

'*'.Repeat(5)   // "*****"
'x'.AsString()  // "x"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.50%. Comparing base (667c235) to head (972c091).
⚠️ Report is 2 commits behind head on prime.

Additional details and impacted files

@@            Coverage Diff             @@
##            prime      #40      +/-   ##
==========================================
+ Coverage   94.47%   94.50%   +0.03%     
==========================================
  Files          76       78       +2     
  Lines        1574     1583       +9     
  Branches      131      131              
==========================================
+ Hits         1487     1496       +9     
  Misses         65       65              
  Partials       22       22              

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[Copilot]

Pull request overview

Adds char extension helpers to PowerKit (ported from CliFx) to simplify generating strings from single characters and repeated characters.

Changes:

• Introduces CharExtensions with Repeat(int count) and AsString().
• Adds unit tests covering both new extension methods.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
PowerKit/Extensions/CharExtensions.cs	Adds char extensions for repeating a character into a string and converting a char to a single-character string.
PowerKit.Tests/CharExtensionsTests.cs	Adds tests validating expected outputs for Repeat (including 0) and AsString.

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