Dev: Add Zeller's Congruence utility class to calculate the day of the week

[BanulaKumarage]

• 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 76.60%. Comparing base (3c071c4) to head (fbb3f57).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6614      +/-   ##
============================================
+ Coverage     76.56%   76.60%   +0.03%     
- Complexity     6015     6025      +10     
============================================
  Files           718      719       +1     
  Lines         20292    20326      +34     
  Branches       3935     3937       +2     
============================================
+ Hits          15537    15570      +33     
  Misses         4164     4164              
- Partials        591      592       +1     

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[BanulaKumarage]

Hi @alxkm, could you please review this PR?

[BanulaKumarage]

@DenizAltunkapan, thanks for approving the PR. Can you merge this?