Added ElGamal Encryption Algorithm (Cryptography)

[Shewale41]

🧾 Pull Request — ElGamal Encryption Algorithm

✅ Declaration

• 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 similar explanations.
• All new code is formatted using:

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.35802% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.41%. Comparing base (21eff8a) to head (b48f2f4).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
...ithms/datastructures/trees/ThreadedBinaryTree.java	90.19%	2 Missing and 3 partials ⚠️
...a/com/thealgorithms/ciphers/ElGamalEncryption.java	88.88%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7002      +/-   ##
============================================
+ Coverage     78.26%   78.41%   +0.14%     
- Complexity     6573     6641      +68     
============================================
  Files           743      750       +7     
  Lines         21895    22096     +201     
  Branches       4288     4331      +43     
============================================
+ Hits          17137    17326     +189     
- Misses         4074     4081       +7     
- Partials        684      689       +5     

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