refactor: Enhance docs, add tests in ReverseKGroup

[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 73.11%. Comparing base (94fb92e) to head (60284d7).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5999   +/-   ##
=========================================
  Coverage     73.11%   73.11%           
- Complexity     5039     5040    +1     
=========================================
  Files           655      655           
  Lines         17594    17593    -1     
  Branches       3389     3389           
=========================================
  Hits          12864    12864           
  Misses         4235     4235           
+ Partials        495      494    -1     

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