You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: txn_list_append_multi.rs
    path of file: ./repos/materialize/src/persist-cli/src/maelstrom
    
    the code of the file until where you have to start completion: // Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.

//! An implementation of the Maelstrom txn-list-append workload using the
//! multi-shard txn abstraction.

use std::collections::btree_map::Entry;
use std::collections::hash_map::DefaultHasher;
use std::collections::{BTreeMap, BTreeSet};
use std::hash::{Hash, Hasher};
use std::sync::Arc;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

use async_trait::async_trait;
use differential_dataflow::consolidation::consolidate_updates;
use
    
    async fn eval(&self, handle: Handle, src: NodeId, req: Body) {
        match req {
            Body::ReqTxn { msg_id, txn } => {
                let in_reply_to = msg_id;
                match self.0.lock().await.transact(&txn).await {
                    Ok(txn) => handle.send_res(src, |msg_id| Body::ResTxn {
                        msg_id,
                        in_reply_to,
                        txn,
                    }),
                    Err(MaelstromError { code, text }) => {
                        handle.send_res(src, |msg_id| Body::Error {
                            msg_id: Some(msg_id),
                            in_reply_to,
                            code,
                            text,
                        })
                    }
                }
            }
            req => unimplemented!("unsupported req: {:?}", req),
        }
    }