refactor: cleanup `RadixSort` (#5280)

* refactor: refactoring RadixSort, adding test, update DIRECTORY.md

* checkstyle: fix formatting for test

* refactor: adding possibility to sort negative numbers. Improve tests. Improving code readability

* checkstyle: fix formatting

* refactor: resolve conflicts with master branch

* refactor: remove negative integers support

* checkstyle: fix formatting

* checkstyle: fix formatting, revert test

* refactor: adding return array to countDigits and buildOutput method, adding more specific description to javadocs

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