refactor: Add tests, fix `removeEdge` bug in `MatrixGraphs`

[Hardvan]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 72.13%. Comparing base (a8b8420) to head (c20f7c2).

Files with missing lines	Patch %	Lines
...algorithms/datastructures/graphs/MatrixGraphs.java	92.30%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5968      +/-   ##
============================================
+ Coverage     71.71%   72.13%   +0.41%     
  Complexity     4947     4947              
============================================
  Files           650      650              
  Lines         17560    17560              
  Branches       3385     3385              
============================================
+ Hits          12594    12667      +73     
+ Misses         4492     4414      -78     
- Partials        474      479       +5     

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