append(node) {
    this.nodesMap[node.key] = node;

    if (!this.head.next) {
      // First node to append.
      this.head.next = node;
      this.tail.prev = node;
      node.prev = this.head;
      node.next = this.tail;
    } else {
      // Append to an existing tail.
      const oldTail = this.tail.prev;
      oldTail.next = node;
      node.prev = oldTail;
      node.next = this.tail;
      this.tail.prev = node;
    }

    this.size += 1;

    if (this.size > this.capacity) {
      this.evict(this.head.next);
    }
  }
Appends a new node to the end of the cache linked list.
@param {LinkedListNode} node