Given the root of a binary tree and a node u in the tree, return the nearest node on the same level that is to the right of u, or return null if u is the rightmost node in its level. Example 1: Input: root = [1,2,3,null,4,5,6], u = 4 Output: 5 Explanation: The nearest node on the same level to the right of node 4 is node 5. Example 2: Input: root = [3,null,4,2], u = 2 Output: null Explanation: There are no nodes to the right of 2. Example 3: Input: root = [1], u = 1 Output: null Example 4: Input: root = [3,4,2,null,null,null,1], u = 4 Output: 2 Constraints: The number of nodes in the tree is in the range [1, 105]. 1 <= Node.val <= 105 All values in the tree are distinct. u is a node in the binary tree rooted at root.