feat: Enhanced Singleton and Factory pattern example with thread-safe…

[Shreekant-Bharti]

…ty, dynamic registration, and logging

This PR enhances the existing implementation of the Singleton and Factory Method design patterns by making them more robust, extensible, and aligned with real-world usage. It improves the structure, documentation, and maintainability of the code — turning a simple pattern demo into a clean, production-ready educational example.

📝 Description

Brief description of changes made.

🎃 Hacktoberfest 2025

• This PR is for Hacktoberfest 2025

🎯 Type of Change

• 📝 Documentation update
• 🐛 Bug fix
• ✨ New feature
• 🎨 Code example/tutorial
• 🧪 Testing
• 🔧 Code refactoring

📋 Difficulty Level

• Beginner
• Intermediate
• Advanced

✅ Checklist

• My code follows the style guidelines
• I have performed a self-review
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

🧪 Testing

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📸 Screenshots (if applicable)

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📎 Additional Notes

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