Added ElGamal Encryption Algorithm

[Shewale41]

• I have read CONTRIBUTING.md
• Code follows TheAlgorithms/Java package structure and naming conventions
• SpotBugs, Checkstyle, and CodeQL pass
• Javadoc comments added for all public methods and classes
• Added JUnit test cases for validation
• Verified encryption-decryption correctness
• Code formatted with clang-format

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.56627% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.40%. Comparing base (21eff8a) to head (33146c6).
⚠️ 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	90.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7006      +/-   ##
============================================
+ Coverage     78.26%   78.40%   +0.13%     
- Complexity     6573     6641      +68     
============================================
  Files           743      750       +7     
  Lines         21895    22098     +203     
  Branches       4288     4331      +43     
============================================
+ Hits          17137    17326     +189     
- Misses         4074     4082       +8     
- Partials        684      690       +6     

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[github-actions]

This pull request has been automatically closed because its workflows or checks failed and it has been inactive for more than 14 days. Please fix the workflows and reopen if you'd like to continue. Merging from main/master alone does not count as activity.