refactor: Enhance docs, add tests in `GenericHeap`

[Hardvan]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• [x] 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 :white_check_mark:

Project coverage is 73.12%. Comparing base (63d13b6) to head (ef5c734).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5980      +/-   ##
============================================
+ Coverage     73.11%   73.12%   +0.01%     
  Complexity     5039     5039              
============================================
  Files           655      655              
  Lines         17590    17594       +4     
  Branches       3389     3389              
============================================
+ Hits          12861    12866       +5     
+ Misses         4238     4234       -4     
- Partials        491      494       +3     

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