Fix issue #534: Modernization and refactoring: C# codebase does not leverage latest C# features

[ngtduc693]

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• [] I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Comments in areas I changed are up to date
• I have added comments to hard-to-understand areas of my code
• I have made corresponding changes to the README.md

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.19%. Comparing base (b47cdc9) to head (72a05b3).

Files with missing lines	Patch %	Lines
Algorithms/Other/Luhn.cs	69.23%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #534      +/-   ##
==========================================
- Coverage   95.22%   95.19%   -0.04%     
==========================================
  Files         274      274              
  Lines       10910    10899      -11     
  Branches     1535     1534       -1     
==========================================
- Hits        10389    10375      -14     
- Misses        397      399       +2     
- Partials      124      125       +1     

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