Given the `root` node of a binary search tree and two integers `low` and `high`, return the sum of values of all nodes with a value in the inclusive range `[low, high]`.

Example 1:

    Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
    Output: 32
    Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.

Example 2:

    Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
    Output: 23
    Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 23.

Constraints:

- The number of nodes in the tree is in the range `[1, 2 * 104]`.
- `1 <= Node.val <= 105`
- `1 <= low <= high <= 105`
- All `Node.val` are unique.