Finish the method definition given below.
Given multiple number arguments, the method sum_dig_prod shoud add the numbers passed as arguments. It should then multiply the digits of this sum until
the product is only 1 digit long and return the final product as the result.
- For example: sum_dig_prod(16, 28) ➞ 6
- 16 + 28 = 44
- 4 * 4 = 16
- 1 * 6 = 6