Add engaging APIs for testing, development, and content enhancement

[tanayvasishtha]

Summary

Three high-value free APIs were added to the Test Data & Mock APIs section.

APIs Added

• Cat Facts API - Random cat facts for fun content (no auth required)
• CoinGecko API - Cryptocurrency market data (no auth required)
• Advice Slip API - Random advice and quotes (no auth required)

Why These APIs Are Valuable

• All APIs tested and currently working
• No authentication required (perfect for beginners and testing)
• Fill gaps in the Test Data & Mock APIs section
• Provide diverse content types (entertainment, financial, motivational)
• Great for learning API integration and building engaging applications

Quality Assurance

• ✅ All APIs tested and responding correctly
• ✅ Followed exact repository format and structure
• ✅ Added to appropriate section (Test Data & Mock APIs)
• ✅ Consistent with existing entry style and detail level

[pratik-mahalle]

Hey @tanayvasishtha, Thank you for raising the pr. I am sure this will help the people

[pratik-mahalle]

Hey @tanayvasishtha, Thank you for raising the pr. I am not sure why you add these api in the test data section. Can you please add that in their respective section