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 (d717ca4) to head (fffc89c).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7022   +/-   ##
=========================================
  Coverage     78.33%   78.34%           
- Complexity     6638     6643    +5     
=========================================
  Files           748      749    +1     
  Lines         22100    22110   +10     
  Branches       4340     4341    +1     
=========================================
+ Hits          17311    17321   +10     
  Misses         4091     4091           
  Partials        698      698           

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