feat: add --result as undocumented alias for --results

[Copilot]

Adds --result as a legacy/alias form of --results for users who may omit the trailing s. The alias is intentionally undocumented (no README or user-guide changes).

Description

• Context.cs — Added case "--result": fall-through before case "--results": in the ArgumentParser switch, so both spellings resolve to the same ResultsFile assignment.
• ContextTests.cs — Added Context_Create_ResultAliasFlag_SetsResultsFile to verify --result <file> correctly sets ResultsFile.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code quality improvement

Pre-Submission Checklist

Build and Test

• Code builds successfully: dotnet build --configuration Release
• All unit tests pass: dotnet test --configuration Release
• Self-validation tests pass:
  dotnet run --project src/DemaConsulting.FileAssert --configuration Release --framework net10.0
--no-build -- --validate
• Code produces zero warnings

Code Quality

• New code has appropriate XML documentation comments
• Static analyzer warnings have been addressed

Quality Checks

• All linters pass: ./lint.sh (Unix/macOS) or cmd /c lint.bat / ./lint.bat (Windows)

Testing

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

Documentation

• Updated README.md (if applicable) — no changes intentional; alias is undocumented

Additional Notes

The alias is a silent convenience; it is deliberately excluded from the README and user guide to avoid advertising it as a supported flag.

[Copilot]

Pull request overview

Adds an undocumented CLI alias --result for the existing --results option to preserve compatibility with users who omit the trailing s.

Changes:

• Added --result as a fall-through alias to the --results argument parsing branch.
• Added a unit test asserting --result <file> sets ResultsFile.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/DemaConsulting.FileAssert/Cli/Context.cs	Adds --result case to route to the existing --results handling and ResultsFile assignment.
test/DemaConsulting.FileAssert.Tests/Cli/ContextTests.cs	Adds a new unit test validating --result sets ResultsFile.

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