Test generator functions

[eallender]

Description:
Verify that generator functions (those using yield) work correctly. Consider if they should have a Yields: section instead of or in addition to Returns:.

Test cases:

def generate_numbers(n: int) -> Generator[int, None, None]:
    """
    Should this have Yields or Returns section?
    """
    for i in range(n):
        yield i

Implementation notes:

• PEP 257 doesn't specifically mention generators
• Google/NumPy style guides use Yields: section
• Could detect generator functions and use Yields: instead of Returns:
• Or keep current behavior (Returns) for simplicity