feat(skills): expand fuzz_has_formatting_variation to cover all formatting properties (#1143)

[PratikWayase]

Description

Expanded the fuzz_has_formatting_variation fuzz target to cover all formatting properties used by _has_formatting_variation.

Previously, the fuzz harness only exercised:

• font.name
• font.bold
• font.italic

This PR adds coverage for:

• font.underline
• font.color.rgb
• font.size

Also added corpus seed files under tests/corpus/ to improve fuzzing effectiveness and broaden input coverage.

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Related Issue(s)

Fixes #1143

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Type of Change

Select all that apply:

Code & Documentation:

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Documentation update

Infrastructure & Configuration:

• GitHub Actions workflow
• Linting configuration (markdown, PowerShell, etc.)
• Security configuration
• DevContainer configuration
• Dependency update

AI Artifacts:

• Reviewed contribution with prompt-builder agent and addressed all feedback
• Copilot instructions (.github/instructions/*.instructions.md)
• Copilot prompt (.github/prompts/*.prompt.md)
• Copilot agent (.github/agents/*.agent.md)
• Copilot skill (.github/skills/*/SKILL.md)

Other:

• Script/automation (.py)
• Other (please describe):

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Testing

• Ran:

  uv run pytest .github/skills/experimental/powerpoint/tests/fuzz_harness.py -v

• All tests passing (28/28)

• Verified coverage for:

  • underline variation
  • color.rgb variation
  • size variation

• Confirmed fuzz harness works in pytest mode and is compatible with Atheris fuzzing

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Checklist

Required Checks

• Documentation is updated (if applicable)
• Files follow existing naming conventions
• Changes are backwards compatible (if applicable)
• Tests added for new functionality (if applicable)

AI Artifact Contributions

• Used /prompt-analyze to review contribution
• Addressed all feedback from prompt-builder review
• Verified contribution follows common standards and type-specific requirements

Required Automated Checks

• Markdown linting: npm run lint:md
• Spell checking: npm run spell-check
• Frontmatter validation: npm run lint:frontmatter
• Skill structure validation: npm run validate:skills
• Link validation: npm run lint:md-links
• PowerShell analysis: npm run lint:ps
• Plugin freshness: npm run plugin:generate

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Security Considerations

• This PR does not contain any sensitive or NDA information
• Any new dependencies have been reviewed for security issues
• Security-related scripts follow the principle of least privilege

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Additional Notes

• Added corpus seed files for improved fuzz coverage
• Covers all 6 formatting properties as required by issue
• Aligns with feedback from PR feat(skills): add Atheris fuzz harness with CI workflow integration #1102 review

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