max_prime to 0 to keep track of the largest prime number found on the diagonals.i from 0 to the length of nums minus 1.
i, check if nums[i][i] (main diagonal) is a prime number. If it is, update max_prime if it's larger than the current max_prime.nums[i][nums.length - i - 1] (secondary diagonal) is a prime number. If it is, update max_prime if it's larger than the current max_prime.max_prime as the result.