feat: implement quicksort algorithm

Summary

This MR adds a complete implementation of the quicksort algorithm with two different approaches:

Implementations

1. quicksort() - Recursive implementation using list comprehensions

   • Returns a new sorted list
   • Simple and easy to understand
   • Uses pivot selection from middle element

2. quicksort_inplace() - In-place implementation using Lomuto partition scheme

   • Sorts the list in-place
   • More memory efficient (O(log n) space)
   • Uses last element as pivot

Features

• ✅ Both implementations handle all edge cases (empty list, single element, etc.)
• ✅ Comprehensive test suite with 13 test cases
• ✅ All tests pass successfully
• ✅ Both implementations produce identical results
• ✅ Well-documented code with docstrings

Test Coverage

• Empty list
• Single element list
• Already sorted list
• Reverse sorted list
• Random list
• List with duplicate elements
• Consistency between both implementations

Performance

• Time complexity: O(n log n) average, O(n²) worst-case
• Space complexity: O(n) for quicksort(), O(log n) for quicksort_inplace()

This implementation is ready for production use and follows best practices for algorithm implementation.