feat(bst): Implement BinarySearchTree, including Enumerable and Countable#4

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fgm wants to merge 5 commits intomainfrom bst

+563-3

Commits on May 13, 2022

feat(bst): working except delete not implemented.
fgm
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Commits on May 14, 2022

Commits on May 15, 2022

chore(bst): 100% coverage with cancelable walks, IndexOf.
fgm
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