Given a `m x n` matrix `mat` and an integer `threshold`, return the maximum side-length of a square with a sum less than or equal to `threshold` or return `0` if there is no such square.

Example 1:

    Input: mat = [[1,1,3,2,4,3,2],[1,1,3,2,4,3,2],[1,1,3,2,4,3,2]], threshold = 4
    Output: 2
    Explanation: The maximum side length of square with sum less than 4 is 2 as shown.

Example 2:

    Input: mat = [[2,2,2,2,2],[2,2,2,2,2],[2,2,2,2,2],[2,2,2,2,2],[2,2,2,2,2]], threshold = 1
    Output: 0

Constraints:

- `m == mat.length`
- `n == mat[i].length`
- `1 <= m, n <= 300`
- `0 <= mat[i][j] <= 104`
- `0 <= threshold <= 105`