Improve documentation and inline comments for QuickSort algorithm

[Harshit-0413]

This PR improves the QuickSort implementation by adding detailed JavaDoc and
inline comments explaining pivot selection, partitioning logic, recursive
steps, and time/space complexity.

Fixes #7143

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.90%. Comparing base (bb33488) to head (dd287b0).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7182   +/-   ##
=========================================
  Coverage     78.90%   78.90%           
+ Complexity     6864     6863    -1     
=========================================
  Files           772      772           
  Lines         22697    22697           
  Branches       4459     4459           
=========================================
+ Hits          17908    17909    +1     
+ Misses         4073     4072    -1     
  Partials        716      716           

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[DenizAltunkapan]

@Harshit-0413 please format your code

[Harshit-0413]

Thanks for the review! I’ve formatted the code and fixed the JavaDoc layout.