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: load_generator.rs
    path of file: ./repos/materialize/src/storage-types/src/sources
    
    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.

//! Types related to load generator sources

use mz_ore::now::NowFn;
use mz_proto::{RustType, TryFromProtoError};
use mz_repr::adt::numeric::NumericMaxScale;
use mz_repr::{ColumnType, GlobalId, RelationDesc, Row, ScalarType};
use once_cell::sync::Lazy;
use proptest_derive::Arbitrary;
use serde::{Deserialize, Serialize};
use std::collections::BTreeSet;

use crate::sources::{MzOffset, SourceConnection};

include!(concat!(
    env!("OUT_DIR"),
    "/mz_storage_types.sources.load_generator.rs"
));

/// Data and progress events of the native stream.
pub enum Event<F: IntoIterator, D> {
    /// Indicates that timestamps have advanced to frontier F
    Progress(F),
    /// Indicates that event D happened at time T
    Message(F::Item, D),
}

#[derive(Arbitrary, Clone, Debug, E
    
    fn from_proto(proto: ProtoLoadGeneratorSourceConnection) -> Result<Self, TryFromProtoError> {
        use proto_load_generator_source_connection::Kind;
        let kind = proto.kind.ok_or_else(|| {
            TryFromProtoError::missing_field("ProtoLoadGeneratorSourceConnection::kind")
        })?;
        Ok(LoadGeneratorSourceConnection {
            load_generator: match kind {
                Kind::Auction(()) => LoadGenerator::Auction,
                Kind::Counter(ProtoCounterLoadGenerator { max_cardinality }) => {
                    LoadGenerator::Counter { max_cardinality }
                }
                Kind::Marketing(()) => LoadGenerator::Marketing,
                Kind::Tpch(ProtoTpchLoadGenerator {
                    count_supplier,
                    count_part,
                    count_customer,
                    count_orders,
                    count_clerk,
                }) => LoadGenerator::Tpch {
                    count_supplier,
                    count_part,
                    count_customer,
                    count_orders,
                    count_clerk,
                },
                Kind::Datums(()) => LoadGenerator::Datums,
            },
            tick_micros: proto.tick_micros,
        })
    }