refactor: Enhance docs, add tests in `MaxHeap`

[Hardvan]

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• [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

Attention: Patch coverage is 82.60870% with 8 lines in your changes missing coverage. Please review.

Project coverage is 72.71%. Comparing base (d1c1e6b) to head (eb6981a).

Files with missing lines	Patch %	Lines
...om/thealgorithms/datastructures/heaps/MaxHeap.java	82.60%	2 Missing and 6 partials :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5983      +/-   ##
============================================
+ Coverage     72.39%   72.71%   +0.31%     
- Complexity     4988     5025      +37     
============================================
  Files           654      654              
  Lines         17586    17603      +17     
  Branches       3388     3392       +4     
============================================
+ Hits          12732    12800      +68     
+ Misses         4372     4316      -56     
- Partials        482      487       +5     

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