Add TrimPrefix/TrimSuffix string extensions for segment-based trimming

[Copilot]

string.TrimStart/TrimEnd/Trim operate on character sets, not substrings. This adds segment-aware counterparts that strip a specific prefix or suffix string once if present.

Changes

• TrimPrefix(string prefix, StringComparison = Ordinal) — removes the leading substring if the string starts with it; otherwise returns the original unchanged
• TrimSuffix(string suffix, StringComparison = Ordinal) — removes the trailing substring if the string ends with it; otherwise returns the original unchanged

Names intentionally avoid TrimStart/TrimEnd to prevent silent mismatch with the BCL overloads that accept ReadOnlySpan<char> (to which string implicitly converts).

Example

"https://example.com".TrimPrefix("https://")   // "example.com"
"archive.tar.gz".TrimSuffix(".gz")             // "archive.tar"
"Archive.TAR.GZ".TrimSuffix(".gz", StringComparison.OrdinalIgnoreCase) // "Archive.TAR"

// No match — original returned unchanged
"example.com".TrimPrefix("https://")  // "example.com"

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.25%. Comparing base (b455fa3) to head (98b8262).

Additional details and impacted files

@@            Coverage Diff             @@
##            prime      #87      +/-   ##
==========================================
+ Coverage   86.23%   86.25%   +0.02%     
==========================================
  Files          74       74              
  Lines        1242     1244       +2     
  Branches      229      231       +2     
==========================================
+ Hits         1071     1073       +2     
  Misses        121      121              
  Partials       50       50              

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[Copilot]

Pull request overview

Adds segment-aware string trimming helpers to PowerKit.Extensions.StringExtensions to complement TrimStart/TrimEnd/Trim, which operate on character sets rather than substrings.

Changes:

• Added TrimPrefix(string prefix, StringComparison comparison = Ordinal) to remove a single matching leading substring.
• Added TrimSuffix(string suffix, StringComparison comparison = Ordinal) to remove a single matching trailing substring.
• Added unit tests covering matching/non-matching cases, empty prefix/suffix, and OrdinalIgnoreCase behavior.

Reviewed changes

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

File	Description
PowerKit/Extensions/StringExtensions.cs	Introduces TrimPrefix/TrimSuffix extension methods implemented via StartsWith/EndsWith + slicing.
PowerKit.Tests/Extensions/StringExtensionsTests.cs	Adds test coverage for the new trimming methods, including case-insensitive comparisons and edge cases.

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