refactor: cleanup GenerateSubsets

[alxkm]

• Added JavaDocs to class and methods
• Renamed doRecursion to generateSubsets for clarity
• Improved variable names for readability
• Enforced utility class pattern with private constructor
• Added comments to explain recursion logic

• 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 74.64%. Comparing base (910d5b8) to head (70d96fd).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6373   +/-   ##
=========================================
  Coverage     74.64%   74.64%           
+ Complexity     5444     5443    -1     
=========================================
  Files           682      682           
  Lines         18999    18998    -1     
  Branches       3668     3668           
=========================================
  Hits          14181    14181           
+ Misses         4261     4259    -2     
- Partials        557      558    +1     

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[DenizAltunkapan]

Your cleanups are very helpful, especially the lack of javadoc above the class suprises me