[FEATURE] Add implementation of IntroSort in C

[kokatesaurabh]

This PR adds an implementation of the IntroSort (Introspective Sort) algorithm in C.

IntroSort is a hybrid sorting algorithm that combines QuickSort, HeapSort, and InsertionSort.
It begins with QuickSort, switches to HeapSort when recursion depth exceeds a certain limit,
and uses InsertionSort for small partitions. This ensures both fast average-case performance
and worst-case optimality. IntroSort is the algorithm behind std::sort.

Proposed Changes:

• Add introsort.c with the full IntroSort implementation.
• Use QuickSort as the base algorithm.
• Switch to HeapSort if recursion depth exceeds 2 * log2(n) (bit-hack __builtin_clz used for log2).
• Use InsertionSort for subarrays smaller than 16 elements.
• Include helper functions: swap, heapify, printArray, and test cases in main().
• Safe handling of empty and single-element arrays.
• Inline comments detailing time and space complexity.

Benefits:

1. Adds a high-performance, practical sorting algorithm used in real-world systems.
2. Complements existing sorting algorithm collection in the repository.
3. Provides a reference implementation for hybrid sorting strategies.
4. Helps learners understand how QuickSort, HeapSort, and InsertionSort can be combined effectively.

Testing:

• Verified correctness using multiple test cases: random, sorted, reverse-sorted, duplicate elements, single element, and empty array.
• Prints original and sorted arrays for demonstration.

This implementation ensures IntroSort is easy to compile and run on any system without additional dependencies (math.h removed; log2 replaced with bit-hack).

Closes #1488.

[kokatesaurabh]

@Panquesito7 @tjgurwara99 @alexpantyukhin hello can you review my pr!! i would like to contribute in your repository!!