Refine docstring and simplify reverse_letters implementation (#14205) * docs: refine docstring and simplify reverse_letters implementation Updated the docstring for clarity and improved the logic for reversing words. * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Update reverse_letters.py --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>