Implemented recursive merge sort algorithm with O(n log n)

[djeada]

• Implemented recursive merge sort algorithm with O(n log n) time complexity.
• Implemented merge helper function for combining sorted sublists.
• Introduced generate_random_list function to encapsulate list generation logic.
• Created main function with a docstring detailing time complexity.
• Used f-strings for improved readability.
• Enhanced modularity and readability.
• Maintained original functionality and interface for backward compatibility.