feat: Add Kadane's Algorithm for Maximum Subarray

[a18-n03]

Description

Adds Kadane's Algorithm implementation for finding the maximum subarray sum.

Changes

• New file: dynamic_programming/kadanes_algorithm.py
• Includes docstring, type hints, and test cases
• Follows existing code style

Checklist

• Code follows project conventions
• Added docstring with algorithm explanation
• Time complexity: O(n)
• Space complexity: O(1)

[prashantpiyush1111]

@a18-n03 I noticed that dynamic_programming/max_subarray_sum.py already implements Kadane's Algorithm with O(n) time, O(1) space, documentation, and doctests.

Since the issue specifically requests a new dynamic_programming/kadanes_algorithm.py, would you prefer keeping the existing implementation and closing this issue as already covered, or should it be moved/renamed to match the requested filename?