feat: Add Binary Search Tree (BST) and AVL Tree implementations

[Raghu0703]

This PR adds Binary Search Tree (BST) and AVL Tree implementations to the data structures collection.

Changes:

• Implemented BST with insert, delete, search operations
• Implemented AVL Tree with self-balancing rotations (LL, RR, LR, RL)
• Added comprehensive unit tests for both implementations
• Included traversal methods (inorder, preorder, postorder)
• Added proper JavaDoc documentation

These fundamental data structures help demonstrate the difference between basic BST and self-balancing trees, providing educational value for learning algorithm complexity and tree balancing techniques.

Fixes #6957

• 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

❌ Patch coverage is 91.62304% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.62%. Comparing base (f693c44) to head (a1c276c).

Files with missing lines	Patch %	Lines
...om/thealgorithms/datastructures/trees/AVLTree.java	86.20%	7 Missing and 9 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7099      +/-   ##
============================================
+ Coverage     78.50%   78.62%   +0.11%     
- Complexity     6752     6794      +42     
============================================
  Files           759      760       +1     
  Lines         22402    22478      +76     
  Branches       4400     4404       +4     
============================================
+ Hits          17587    17673      +86     
+ Misses         4109     4101       -8     
+ Partials        706      704       -2     

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