Re-implement chaining searchers

[KyouyamaKazusa0805]

There is a thing I have to do for now - re-implement chaining APIs to support grouped nodes.

From the year 2019 (beginning with this repository), I have chosen the algorithm and copied the basic implementation for Sudoku Explainer.

This algorithm has been lived for 5 years. I must say this algorithm is very good one that always makes me satisfied.

"But ~~Xiaolu~~ Sunnie", you might say, "Why you didn't use your own algorithm from the start?"

A rough problem is that, I'm not familiar with algorithm of chains. I just think that the chaining rule is too hard to implement, keeping a good performance.

I want to challenge this in not few weeks.

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翻译：

有一个亟待解决的事情 - 我必须要开始重新实现链的 API 来支持区块节点了。

从 2019 年开始（梦开始的地方），我就选择了一个 Sudoku Explainer 的基础实现作为我的项目的链的基本处理算法。

这个算法在这个项目里存在了 5 年之久。我不得不说这个算法我一直都觉得不错。

不过你可能会问我：“为啥你不最开始就使用你自己的算法呢？”

有一个棘手的问题。我根本不熟悉链的算法。我就觉得这玩意儿有点难实现，而且要保证良好的性能。

我打算要不了几周之后开始挑战这个玩意儿。