- Add Cache struct with entries map, mutex, maxSize, defaultTTL, strategy, and stats fields
- Add CacheStrategy type with LRU, TTL, write-through, write-back, and read-through constants
- Add CacheEntry struct with Key, Value, ExpiresAt, CreatedAt, and HitCount fields
- Add NewCache constructor with CacheConfig parameter and automatic cleanup goroutine
- Add Get, Set, Delete, and Clear methods with hit
