Update binary_search_tree.cpp

[arjunjain8887]

1. Memory Management: Used std::unique_ptr for automatic memory management, reducing the risk of memory leaks.

2. STL Utilization: Replaced the custom queue implementation with std::queue, simplifying breadth-first traversal.

3. Code Structure: Organized the code into a BinaryTree class, encapsulating the tree functionality and providing clearer interfaces for operations.

4. Redundancy Reduction: Combined logic for finding and removing nodes to reduce redundancy, improving readability and maintainability.

5. Error Handling: Added checks to handle cases where nodes may not be present during removal and traversal.

Description of Change

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes: