refactor: Enhance docs, add tests in HeapElement

[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

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 70.89%. Comparing base (08bd1ff) to head (c2d0e63).

Files with missing lines	Patch %	Lines
...healgorithms/datastructures/heaps/HeapElement.java	40.00%	0 Missing and 3 partials :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5981      +/-   ##
============================================
+ Coverage     70.78%   70.89%   +0.11%     
- Complexity     4859     4869      +10     
============================================
  Files           650      650              
  Lines         17533    17529       -4     
  Branches       3379     3378       -1     
============================================
+ Hits          12411    12428      +17     
+ Misses         4658     4634      -24     
- Partials        464      467       +3     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.