Function finalize_proof 

pub fn finalize_proof<F>(
    plan: &ProofPlan,
    leaf: u64,
    lookup: F,
) -> Result<(B256, B256, Vec<B256>), &'static str>
where
    F: Fn(LevelAndLeaf) -> Option<B256>,

Given a resolved map from LevelAndLeaf → hash (fetched from log scan + partials), walk the proof path and return (send, root, proof_vec) ready for ABI encoding.

lookup is the client-supplied closure that maps each node position to its hash (from logs or from accumulator partial state).