Add AVL Tree implementation (insert, delete, balance check)

[darshan-totagi]

This PR adds a complete AVL Tree implementation under com.thealgorithms.tree.AVLTree.

• Removed unnecessary blank lines and trailing newlines
• Simplified single-line if statements for compactness
• Ensured consistent indentation and formatting across:
  • AVLInsert.java
  • AVLDelete.java
  • Rotations.java

All class and package names follow PascalCase and standard Java conventions.

• 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 78.28%. Comparing base (55da3b9) to head (1fcd713).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6973   +/-   ##
=========================================
  Coverage     78.27%   78.28%           
- Complexity     6573     6574    +1     
=========================================
  Files           743      743           
  Lines         21895    21895           
  Branches       4288     4288           
=========================================
+ Hits          17139    17140    +1     
  Misses         4073     4073           
+ Partials        683      682    -1     

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