用内嵌双向链表管理空闲 KV 块

214        if block.prev_free_block is not None:215            # Link the previous block to the next block.216            block.prev_free_block.next_free_block = block.next_free_block217        if block.next_free_block is not None:218            # Link the next block to the previous block.219            block.next_free_block.prev_free_block = block.prev_free_block220221        if block == self.free_list_head:222            # Update the head if the block is the head.223            self.free_list_head = block.next_free_block224        if block == self.free_list_tail:225            # Update the tail if the block is the tail.226            self.free_list_tail = block.prev_free_block227228        # Remove the block from the linked list.229        block.prev_free_block = block.next_free_block = None230        self.num_free_blocks -= 1