input: Write a python function to find the maximum sum subarray using Kadane's algorithm.
  assert max_sum_subarray([-2, 1, -3, 4, -1, 2, 1, -5, 4]) == 6
  assert max_sum_subarray([1, 2, 3, 4, 5]) == 15
  assert max_sum_subarray([-1, -2, -3, -4, -5]) == 0
output: def max_sum_subarray(nums):
      max_current = max_global = nums[0]
      
      for num in nums[1:]:
          max_current = max(num, max_current + num)
          if max_current > max_global:
              max_global = max_current
      
      return max_global