Template cache needs protection against unbounded growth

[willibrandon]

The template cache in internal/parser/cache.go has no size limit or eviction policy, creating a potential memory exhaustion vulnerability.

Issue

Dynamic template generation could cause unbounded memory growth:

for i := 0; i < 1000000; i++ {
    logger.Info(fmt.Sprintf("User %d: {Action}", i), "login")
}

Solution

Implement an LRU cache with:

• Configurable max size (default: 10,000 templates)
• O(1) get/put operations
• Optional TTL support
• Cache hit/miss metrics for monitoring

Benefits

• Prevents memory exhaustion
• Predictable memory usage
• Better performance insights via metrics
• Production-ready for 1.0 release