Python doesn't calculate time for executing a function

Question

I am learning some Python basics and we had this code about wrapper functions and how they can be used to add functionality to wrapped functions. So we calculate time that was used to compute two different functions:

    import time


def timer(fn):
    def wrapper():
        t0 = time.time()
        result = fn()
        dt = time.time() - t0
        return dt

    return wrapper


def pow_2():
    return 10000000 ** 2


def in_build_pow():
    return pow(10000000, 2)


pow_2 = timer(pow_2)
in_build_pow = timer(in_build_pow)

a, b = 0, 0
N = 100
for i in range(N):
    a += pow_2()
    b += in_build_pow()

print("a = ", a)
print("b = ", b)
print(f"Average time pow_2 = {a / N:.10f}")
print(f"Average time in_build_pow = {b / N:.10f}")

But my result looks like this:

Unless I increase the iteration count N to more than 1000. The higher N, the more often results are not 0.0.

This is N = 1000:

And this is N = 10,000:

Does anyone knows why it is like this? Why I cannot count time for fewer iterations? The code works fine in online compilers, though. But VSCode, VS2022, and PyCharm all have same issues for me.