Allow developers to configure 'FetchCount'

Resolves #40

Source/Picton.Messaging/AsyncMessagePump.cs

@@ -475,7 +475,7 @@ private async Task ProcessMessagesAsync(CancellationToken cancellationToken)
 
 							try
 							{
-								messages = await queueInfo.QueueManager.GetMessagesAsync(_messagePumpOptions.ConcurrentTasks, queueInfo.Config.VisibilityTimeout, cancellationToken).ConfigureAwait(false);
+								messages = await queueInfo.QueueManager.GetMessagesAsync(_messagePumpOptions.FetchCount, queueInfo.Config.VisibilityTimeout, cancellationToken).ConfigureAwait(false);
 							}
 							catch (Exception e) when (e is TaskCanceledException || e is OperationCanceledException)
 							{

Source/Picton.Messaging/MessagePumpOptions.cs

@@ -10,6 +10,7 @@ namespace Picton.Messaging
 	public record MessagePumpOptions
 	{
 		private const int _defaultConcurrentTasks = 25;
+		private const int _defaultFetchCount = 10;
 		private static readonly TimeSpan _defaultFetchMessagesInterval = TimeSpan.FromSeconds(1);
 		private static readonly TimeSpan _defaultCountAzureMessagesInterval = TimeSpan.FromSeconds(5);
 		private static readonly TimeSpan _defaultCountMemoryMessagesInterval = TimeSpan.FromSeconds(5);
@@ -54,6 +55,11 @@ public MessagePumpOptions(string connectionString, int? concurrentTasks, QueueCl
 		/// </summary>
 		public int ConcurrentTasks { get; set; } = _defaultConcurrentTasks;
 
+		/// <summary>
+		/// Gets or sets the number of messages fetched per queue.
+		/// </summary>
+		public int FetchCount { get; set; } = _defaultFetchCount;
+
 		/// <summary>
 		/// Gets or sets the optional client options that define the transport
 		/// pipeline policies for authentication, retries, etc., that are applied