refactor: change packages

[alxkm]

Change packages of few classes:

FordFulkerson is a graph algorithm.

KMP and RabinKarp, are string algorithms.

SieveOfEratosthenes and EulersFunction, are mathematical algorithms.

• 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 50.96%. Comparing base (f8ff6af) to head (455a9ae).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5430      +/-   ##
============================================
- Coverage     50.97%   50.96%   -0.02%     
- Complexity     3152     3158       +6     
============================================
  Files           523      523              
  Lines         15104    15104              
  Branches       2874     2874              
============================================
- Hits           7699     7697       -2     
- Misses         7084     7085       +1     
- Partials        321      322       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.