Fixes: #2630 Add doctests and support for negative numbers (#2626)

* add type hints to math/extended euclid

* math/extended euclid - add doctest

* math/extended euclid: remove manual doctest

* change algorithm for negative numbers

* improve naming of variables

* Update extended_euclidean_algorithm.py

Co-authored-by: Dhruv <dhruvmanila@gmail.com>