fix: use unified metrics cache in compare endpoint (#811)

[Vaibhavi-14shetty]

Summary

This PR refactors the compare metrics endpoint to use the unified caching implementation from metrics-cache.ts, ensuring consistent cache usage across metric-related APIs and eliminating redundant or endpoint-specific caching logic.

Closes #811

Changes Made

• Updated src/app/api/metrics/compare/route.ts to use the shared metrics cache instead of local or duplicated caching logic
• Refactored src/lib/metrics-cache.ts to support unified cache access for compare endpoint usage
• Ensured consistent cache key usage and retrieval flow across metric requests
• Removed redundant caching implementation in the compare endpoint

How to Test

1. Run the development server
2. Call the compare metrics API with identical inputs multiple times
3. Verify that subsequent requests return cached responses
4. Confirm no duplicate external metric fetches occur

Checklist

• Linked issue (fix : use unified metrics cache in compare endpoint #811)
• Self-reviewed the diff
• No unintended changes (e.g., package-lock.json removed)

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[Vaibhavi-14shetty]

Hello @Priyanshu-byte-coder, I’ve completed the changes for this issue #811
Please review my PR when you get time. Let me know if any changes are needed.

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