refactor: Enhance docs, code, add tests in LeonardoNumber

[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 77.34%. Comparing base (883a050) to head (23d96b2).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6743      +/-   ##
============================================
+ Coverage     77.33%   77.34%   +0.01%     
- Complexity     6171     6176       +5     
============================================
  Files           721      721              
  Lines         20589    20600      +11     
  Branches       3992     3994       +2     
============================================
+ Hits          15922    15933      +11     
  Misses         4055     4055              
  Partials        612      612              

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[DenizAltunkapan]

thanks