refactor: Enhance docs, add tests in MajorityElement

[Hardvan]

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

Project coverage is 67.98%. Comparing base (5246f63) to head (91ee125).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #5978   +/-   ##
=========================================
  Coverage     67.98%   67.98%           
- Complexity     4586     4587    +1     
=========================================
  Files           620      620           
  Lines         17116    17116           
  Branches       3305     3305           
=========================================
  Hits          11636    11636           
  Misses         5035     5035           
  Partials        445      445           

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