[3.12] gh-112182: Replace StopIteration with RuntimeError for future (GH-113220) (GH-123033)

When an `StopIteration` raises into `asyncio.Future`, this will cause
a thread to hang. This commit address this by not raising an exception
and silently transforming the `StopIteration` with a `RuntimeError`,
which the caller can reconstruct from `fut.exception().__cause__`
(cherry picked from commit 4826d52338396758b2d6790a498c2a06eec19a86)

Co-authored-by: Jamie Phan <jamie@ordinarylab.dev>