Doctest Error Correction of mirror_formulae.py (#9782)

* Python mirror_formulae.py is added to the repository

* Changes done after reading readme.md

* Changes for running doctest on all platforms

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

for more information, see https://pre-commit.ci

* Change 2 for Doctests

* Changes for doctest 2

* updating DIRECTORY.md

* Doctest whitespace error rectification to mirror_formulae.py

* updating DIRECTORY.md

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: Christian Clauss <[email protected]>