Added one time pad cipher

[Shewale41]

Added One-Time Pad Cipher Implementation

This pull request adds an implementation of the One-Time Pad Cipher under the ciphers package.
The One-Time Pad Cipher is a symmetric encryption technique that XORs plaintext with a random key of equal length, providing perfect secrecy when the key is truly random and used only once.

Features:

• Uses SecureRandom for key generation.
• Provides methods for both encryption and decryption using XOR.
• Includes JavaDoc with reference to the official algorithm documentation.

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 include a reference link in their comments.
All code is formatted with clang-format -i --style=file path/to/your/file.java.

File Added:
src/main/java/com/thealgorithms/ciphers/OneTimePadCipher.java

---

Fixes issue: #6941

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.19%. Comparing base (21eff8a) to head (1e78a3f).

Files with missing lines	Patch %	Lines
...va/com/thealgorithms/ciphers/OneTimePadCipher.java	0.00%	22 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6966      +/-   ##
============================================
- Coverage     78.26%   78.19%   -0.08%     
  Complexity     6573     6573              
============================================
  Files           743      744       +1     
  Lines         21895    21917      +22     
  Branches       4288     4290       +2     
============================================
  Hits          17137    17137              
- Misses         4074     4096      +22     
  Partials        684      684              

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