Implement LRU (Least Recently Used) Cache Policy

[0xnullifier]

What is LRU?
LRU is a cache policy that removes the least recently used items when space is needed
Technical Requirements:

1. Create a new struct LRUCachePolicy that implements the CachePolicy interface
2. Use a data structure to keep track of things efficiently maybe something like doubly-linked list + hashmap to track access order efficiently
3. Implement both required methods:

• Eject(m *Memoria, requiredSpace uint64) error
• Insert(m *Memoria, key string, val []byte) error

NOTE You are welcome to use libraries for data structures but in that case this will be scored as a MEDIUM

Example Structure:

type lruNode struct {
   key  string
   next *lruNode
   prev *lruNode
}

type LRUCachePolicy struct {
   nodeMap map[string]*lruNode
   head    *lruNode  
   tail    *lruNode 
}