This PR introduces an implementation of the IntroSort (Introspective Sort) algorithm in C++ as a new sorting method under sorting/intro_sort.cpp.

IntroSort is a hybrid sorting algorithm combining QuickSort, HeapSort, and InsertionSort to achieve both fast average-case performance and optimal worst-case guarantees. It starts with QuickSort, switches to HeapSort when recursion depth exceeds a limit (2 * log₂(n)), and uses InsertionSort for small partitions (≤ 16 elements).

The implementation includes:

• QuickSort base with Lomuto partition scheme
• Depth-limit detection to switch to HeapSort and avoid QuickSort’s worst-case
• InsertionSort for small subarrays to optimize performance
• Comments explaining time and space complexity
• Sample test cases in main() to verify correctness on various inputs (best, average, worst cases)

This addition enhances the repository by providing a practical, industrial-strength sorting algorithm, complements existing sorting algorithms, and serves as an educational reference for hybrid sorting strategies.

Closes #3010.