[桑基图] 优化桑基图 cutoffcircle 逻辑，降低时间复杂度

[liuzhenying]

桑基图数据量超过 400 时渲染基本卡死，发现大部分耗时在 cutoffcircle 函数上

根据 DFS 算法优化了下逻辑，(参考 https://leetcode-cn.com/problems/course-schedule/solution/course-schedule-tuo-bu-pai-xu-bfsdfsliang-chong-fa/ )，时间复杂度降为 O(n^2)

同样的数据，耗时从 19053 减少为 1

（circle 文件因单测覆盖率已达到 100%，此次未增加测试用例）

PR includes

• fixed #0
• add / modify test cases
• documents, demos

Screenshot

Before	After
❌	✅

[coveralls]

Pull Request Test Coverage Report for Build 870400895

• 38 of 38 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 96.177%

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Files with Coverage Reduction	New Missed Lines	%
src/utils/transform/word-cloud.ts	1	97.75%

Totals
Change from base Build 859961788:	-0.01%
Covered Lines:	5639
Relevant Lines:	5717

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💛 - Coveralls

[hustcc]

之前的时间复杂度算是多少？

[liuzhenying]

之前的时间复杂度算是多少？

没具体算，看了下大概是 O（n^M）, M 为连成线的节点数量，主要是耗在了 hasCircle 内部的递归，递归数量随节点增多直线上升