refactor: Enhance docs, add tests in `MajorityElement`

[Hardvan]

trafficstars

• [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 71.07%. Comparing base (7e87e58) to head (5ae7636).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5978   +/-   ##
=========================================
  Coverage     71.07%   71.07%           
  Complexity     4879     4879           
=========================================
  Files           650      650           
  Lines         17529    17529           
  Branches       3378     3378           
=========================================
  Hits          12459    12459           
  Misses         4599     4599           
  Partials        471      471           

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