refactor: FordFulkerson

[alxkm]

Class cleanup.
Readability improvements.
Added tests.

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.14%. Comparing base (e5c0e4b) to head (ffc9652).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5384      +/-   ##
============================================
+ Coverage     46.92%   47.14%   +0.22%     
- Complexity     2903     2912       +9     
============================================
  Files           525      525              
  Lines         15364    15345      -19     
  Branches       2908     2907       -1     
============================================
+ Hits           7209     7234      +25     
+ Misses         7854     7809      -45     
- Partials        301      302       +1     

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