Removed all caching and logging functionality from prisma.ts, keeping only
the basic Prisma client initialization logic. This includes:
- Removal of getProblems, getCachedProblems, getProblem, getCachedProblem functions
- Removal of related logger and cache imports
- Simplified the global prisma client instantiation
- Add 'server-only' import to enforce server-side usage
- Implement cached problem queries with logging:
- Add getProblems/getCachedProblems for all problems
- Add getProblem/getCachedProblem for single problem by ID
- Use React cache and Next.js unstable_cache with tags
- Add detailed logging with timing metrics
