Added/Improved doctests for lowest_common_ancestor.py (#12673)

* added doctests to functions in lowest_common_ancestor.py

* fixed doctests to be less excessive

* Update lowest_common_ancestor.py

* Update lowest_common_ancestor.py

* Update lowest_common_ancestor.py

* Update lowest_common_ancestor.py

* Update lowest_common_ancestor.py

* Update lowest_common_ancestor.py

---------

Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>