Issue #21: Implement Selection Sort

[Brad-Edwards]

This PR implements the selection sort algorithm with the following features:

• Generic implementation supporting any type implementing Ord + Clone + Debug
• O(n²) time complexity in all cases
• O(1) auxiliary space
• Minimizes the number of swaps (O(n) swaps vs O(n²) comparisons)
• In-place algorithm
• Comprehensive documentation
• Extensive unit tests covering:
  • Empty and single-element arrays
  • Already sorted arrays
  • Reverse sorted arrays
  • Random order arrays
  • Arrays with duplicates
  • Large arrays
  • Arrays with all equal elements
  • Arrays with alternating values
  • Negative numbers
  • Mixed positive and negative numbers
  • Different data types (integers, floats, strings)
  • Verification of O(n) swaps property

Key advantages:

• Simple implementation
• Performs well on small arrays
• Minimal memory writes (good when write cost is high)
• In-place sorting with O(1) extra space