Function apply_leaf 

async fn apply_leaf<T>(
    storage: &Arc<T>,
    instance: &NodeState,
    parent_leaf: &mut Leaf2,
    parent_state: &mut ValidatedState,
    leaf: Leaf2,
)
where
    T: SequencerStateDataSource,
    for<'a> T::Transaction<'a>: SequencerStateUpdate,

Apply leaf to the merklized state, retrying until it is stored, then make it the parent.