/// Unwrap a [`ZstdOutcome`](crate::ZstdOutcome) value, returning the value
/// from the [`Complete`](crate::ZstdOutcome::Complete) variant, or
/// propagating the [`HasMore`](crate::ZstdOutcome::HasMore) variant to the
/// caller (wrapped with `Ok(_)`).
/// Unwrap a [`Poll`](std::task::Poll) value, returning the value from
/// the [`Ready`](std::task::Poll::Ready) variant, or propagating the
/// [`Pending`](std::task::Poll::Pending) variant to the caller.