pub fn get_mut<R>(
        &mut self,
        name: &str,
        mut action: impl FnMut(ShadowMut<'_, Main, Shadow>) -> R,
    ) -> R
    where
        R: PartialEq + fmt::Debug + 'static,
    {
        self.get_custom_mut(name, |r| DivergingEq(action(r))).0
    }
Gets the specified value from both the main and shadow VM, potentially changing their state
and checking whether the returned value matches.
core/lib/vm_interface/src/utils/shadow.rs