feat: implement One-Time Pad cipher (#6941)

[newtownboy]

• Added encryption and decryption functions using One-Time Pad
• Included unit tests for edge cases and invalid inputs

• 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 78.34%. Comparing base (2588af0) to head (7e70a9a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7022      +/-   ##
============================================
- Coverage     78.35%   78.34%   -0.01%     
- Complexity     6671     6675       +4     
============================================
  Files           753      754       +1     
  Lines         22185    22195      +10     
  Branches       4356     4357       +1     
============================================
+ Hits          17382    17389       +7     
- Misses         4105     4106       +1     
- Partials        698      700       +2     

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