Add doctests for the boyer_moore_search algorithm. (#12769)

* Add doctests for the boyer_moore_search algorithm.

* Update boyer_moore_search.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update boyer_moore_search.py

* Update boyer_moore_search.py

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Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>