type LRU[K comparable, V any] struct {
	size      int
	evictList *LruList[K, V]
	items     map[K]*Entry[K, V]
	onEvict   EvictCallback[K, V]

	// expirable options
	mu   sync.RWMutex
	ttl  time.Duration
	done chan struct{}

	// buckets for expiration
	buckets []bucket[K, V]
	// uint8 because it's number between 0 and numBuckets
	nextCleanupBucket uint8
}