You are given a sorted integer array `nums`. Every value appears exactly twice, except for one value that appears exactly once. Find and return the value that appears only once. Requirements: - The algorithm must run in `O(log n)` time. - The algorithm must use `O(1)` extra space. Example 1: ```text Input: nums = [1,1,2,3,3,4,4,8,8] Output: 2 ``` Example 2: ```text Input: nums = [3,3,7,7,10,11,11] Output: 10 ``` Constraints: - `1 <= nums.length <= 100000` - `nums.length` is odd. - The array is sorted in nondecreasing order. - Exactly one element appears once; every other element appears exactly twice.