pub fn upgrade(&self) -> Option<Shared<Fut>> {
        Some(Shared { inner: Some(self.0.upgrade()?), waker_key: NULL_WAKER_KEY })
    }
Attempts to upgrade this [`WeakShared`] into a [`Shared`].

Returns [`None`] if all clones of the [`Shared`] have been dropped or polled
to completion.
futures-util/src/future/future/shared.rs