feat: add karatsuba multiplication

[saahil-mahato]

• 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 62.99%. Comparing base (0ca4398) to head (cd21d29).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5719      +/-   ##
============================================
+ Coverage     62.96%   62.99%   +0.03%     
- Complexity     4048     4051       +3     
============================================
  Files           568      569       +1     
  Lines         16041    16056      +15     
  Branches       3086     3086              
============================================
+ Hits          10100    10115      +15     
  Misses         5525     5525              
  Partials        416      416              

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