You are given an integer array nums. You must perform exactly one operation where you can replace one element nums[i] with nums[i] * nums[i]. Return the maximum possible subarray sum after exactly one operation. The subarray must be non-empty. Example 1: Input: nums = [2,-1,-4,-3] Output: 17 Explanation: You can perform the operation on index 2 (0-indexed) to make nums = [2,-1,16,-3]. Now, the maximum subarray sum is 2 + -1 + 16 = 17. Example 2: Input: nums = [1,-1,1,1,-1,-1,1] Output: 4 Explanation: You can perform the operation on index 1 (0-indexed) to make nums = [1,1,1,1,-1,-1,1]. Now, the maximum subarray sum is 1 + 1 + 1 + 1 = 4. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104