Fix Sonar code smells: static method and test exception patterns

[Copilot]

Pull Request

Description

Addresses Sonar code smells flagged by static analysis: unused instance access (CA1822) and improper exception testing patterns (MSTEST0058).

Production Code

• TraceMatrix.cs: Made SectionHasFilteredContent static (doesn't access instance data)
• Validation.cs: String literal duplication (S1192) suppressed per maintainer preference for inline readability

Test Code

Refactored 49 test methods across 5 files to use MSTest v4's Assert.ThrowsExactly<T>() pattern:

Before:

try
{
    Context.Create(["--results"]);
    Assert.Fail("Expected ArgumentException was not thrown");
}
catch (ArgumentException ex)
{
    Assert.Contains("--results requires a filename argument", ex.Message);
}

After:

var ex = Assert.ThrowsExactly<ArgumentException>(() => Context.Create(["--results"]));
Assert.Contains("--results requires a filename argument", ex.Message);

Pattern applied to:

• ContextTests.cs: 15 methods
• RequirementsReadTests.cs: 28 methods
• RequirementsExportTests.cs: 2 methods
• TraceMatrixExportTests.cs: 2 methods
• TraceMatrixReadTests.cs: 2 methods

Type of Change

• Code quality improvement

Related Issues

Pre-Submission Checklist

Build and Test

• Code builds successfully: dotnet build --configuration Release
• All tests pass: dotnet test --configuration Release
• Code produces zero warnings

Code Quality

• Code formatting is correct: dotnet format --verify-no-changes
• New code has appropriate XML documentation comments
• Static analyzer warnings have been addressed

Quality Checks

• Spell checker passes: cspell "**/*.{md,cs}"
• Markdown linter passes: markdownlint "**/*.md"
• YAML linter passes: yamllint '**/*.{yml,yaml}'

Testing

• Added unit tests for new functionality
• Updated existing tests if behavior changed
• All tests follow the AAA (Arrange, Act, Assert) pattern
• Test coverage is maintained or improved

Documentation

• Updated README.md (if applicable)
• Updated ARCHITECTURE.md (if applicable)
• Added code examples for new features (if applicable)
• Updated requirements.yaml (if applicable)

Additional Notes

CodeQL security scan: No vulnerabilities found. All 132 tests pass.

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