Improved Graph Implementations (TheAlgorithms#8730)

* Improved Graph Implementations

Provides new implementation for graph_list.py and graph_matrix.py along with pytest suites for each. Fixes TheAlgorithms#8709

* Graph implementation style fixes, corrections, and refactored tests

* Helpful docs about graph implementation

* Refactored code to separate files and applied enumerate()

* Renamed files and refactored code to fail fast

* Error handling style fix

* Fixed f-string code quality issue

* Last f-string fix

* Added return types to test functions and more style fixes

* Added more function return types

* Added more function return types pt2

* Fixed error messages

Author: nith2001