Add Segment Tree implementation for Range Minimum Query (RMQ)

[GOURAV-SAHA007]

Description of Change

• Added a new algorithm: Segment Tree Implementation in C++.
• This implementation supports range sum queries and point updates efficiently in O(log N) time.
• The code includes proper documentation, example usage, and test cases.
• The goal of this contribution is to enhance the repository’s data structures section with a well-commented and educational implementation.

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:
This PR introduces a new Segment Tree (Range Sum Query) implementation in C++ under the data_structures folder with detailed comments and example demonstration.