Implement Caching Layer for Analytics API Endpoints

[llinsss]

Many analytics endpoints (e.g., global health trends, aggregated statistics) serve data that doesn't change frequently or requires expensive database queries.
Implement a caching layer (e.g., using Redis with NestJS's @nestjs/cache-manager) for these endpoints to reduce database load, improve response times, and provide a snappier user experience for the frontend.
Define appropriate cache invalidation strategies.