Updated InitializeBuses class with single constructor

InitializeBuses.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Threading.Tasks;
using Sitecore.Diagnostics;
using Sitecore.Events;
using Sitecore.Messaging;
using Sitecore.Messaging.Events;
using Sitecore.Pipelines;

public class InitializeBuses
{
    private readonly IMessageBusStarter _busStarter;

    public InitializeBuses(IMessageBusStarter busStarter)
    {
        _busStarter = busStarter ?? throw new ArgumentNullException(nameof(busStarter));
    }

    public void Process(PipelineArgs args)
    {
        Dictionary<string, bool> busStartResults = new Dictionary<string, bool>();
        _busStarter.Start(
            busName =>
            {
                busStartResults.Add(busName, true);
                Log.Info($"Messaging: IMessageBus started successfully: '{busName}'", this);
                Event.RaiseEvent("messaging:busstarted", new MessageBusInitializedEventArgs(busName, true));
            },
            (busName, ex) =>
            {
                busStartResults.Add(busName, false);
                Log.Error($"Messaging: IMessageBus failed to start '{busName}'.", ex, this);
                Event.RaiseEvent("messaging:busstarted", new MessageBusInitializedEventArgs(busName, false));
            }
        ).ContinueWith(t =>
            Event.RaiseEvent("messaging:allBusesInitialized", new AllMessageBusesInitializedEventArgs(busStartResults)));
    }
}