Fix Cache Reference Error in feeEstimate.js

[Gainer-dev]

Description

This PR fixes a cache reference error in src/routes/feeEstimate.js where the cache service is imported as cacheService but referenced as cache within the route handler. This mismatch results in a ReferenceError whenever cached responses are accessed, preventing the caching layer from functioning correctly.

Changes

• Replaced all cache.get(...) calls with cacheService.get(...).
• Replaced all cache.set(...) calls with cacheService.set(...).
• Restored proper cache access within the /fee-estimate route.
• Ensured cached responses are served without runtime errors.

Why

The incorrect cache reference caused every request that relied on the cache to fail with a ReferenceError, effectively disabling the caching mechanism. This fix restores the intended behavior, improving reliability and performance.

Testing

• Verified GET /fee-estimate returns a successful response without throwing a ReferenceError.
• Confirmed cache misses populate the cache correctly.
• Confirmed subsequent requests return cached responses with the X-Cache: HIT header.
• Verified existing endpoint functionality remains unchanged.

Checklist

• Code follows project standards.
• Tested locally.
• No breaking changes introduced.
• Ready for review.

closes #245
closes #246
closes #247
closes #248

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[Sulex45]

Kindly resolve conflicts