refactor: cleanup DudeneyNumber

[vil02]

This PR cleanups DudeneyNumber and its tests.

• 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 38.25%. Comparing base (cf6c87c) to head (8b4b5ae).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5156      +/-   ##
============================================
- Coverage     38.25%   38.25%   -0.01%     
  Complexity     2361     2361              
============================================
  Files           516      516              
  Lines         15309    15304       -5     
  Branches       2958     2957       -1     
============================================
- Hits           5857     5854       -3     
+ Misses         9165     9164       -1     
+ Partials        287      286       -1     

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[BamaCharanChhandogi]

thanks