Call the generator helper method directly instead of callingPyIter_Next when calling a native generator from a native function. This way we can avoid raising StopIteration when the generator is exhausted. The approach is similar to what I used to speed up calls using await in#19398. Refer to that PR for a more detailed explanation.

This helps mostly when a generator produces a small number of values, which is quite common.

This PR improves the performance of this microbenchmark, which is a close to the ideal use case, by about 2.6x (now 5.7x faster than interpreted):

from typing import Iteratordef foo(x: int) -> Iterator[int]:    for a in range(x):        yield adef bench(n: int) -> None:    for i in range(n):        for a in foo(1):            passfrom time import timebench(1000 * 1000)t0 = time()bench(50 * 1000 * 1000)print(time() - t0)