Triangle Numbers

Complete triangle_number(n: int) -> int so it returns the nth triangle number, the count of dots in a triangle with n rows where row k holds k dots: 1 + 2 + ... + n. This time the recursive case is written for you (n plus the triangle number before it) and the base case is missing: add the check at the top of the body that returns 0 for n equal to 0, so the recursion stops instead of running until Python raises a RecursionError. Do NOT write a main block or any top-level test code; the tests construct the calls. Input: one integer n, no prompt, which the tests read and pass to your function before printing the value it returns.