refactor: cleanup `PigeonholeSort` (#5298)

* refactor: PigeonholeSort

* checkstyle: fix formatting

* checkstyle: make class final

* refactor: changing negative numbers check first, fix typo, adding one more test for negative numbers

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Co-authored-by: Alex Klymenko <alx@alx.com>
Co-authored-by: vil02 <65706193+vil02@users.noreply.github.com>