refactor: Enhance docs, add more tests in JohnsonsAlgorithm

[Hardvan]

• 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 67.43%. Comparing base (be0b1d5) to head (4ec3406).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5964   +/-   ##
=========================================
  Coverage     67.43%   67.43%           
  Complexity     4578     4578           
=========================================
  Files           620      620           
  Lines         17147    17147           
  Branches       3312     3312           
=========================================
  Hits          11563    11563           
  Misses         5138     5138           
  Partials        446      446           

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