nats-io#636 - JetStream Batch Get Client support

* Added batch get contract

src/NATS.Client.JetStream/INatsJSStream.cs

@@ -112,5 +112,15 @@ ValueTask UpdateAsync(
 
     ValueTask<NatsMsg<T>> GetDirectAsync<T>(StreamMsgGetRequest request, INatsDeserialize<T>? serializer = default, CancellationToken cancellationToken = default);
 
+    /// <summary>
+    /// Request a direct batch message
+    /// </summary>
+    /// <param name="request">Batch message request.</param>
+    /// <param name="serializer">Serializer to use for the message type.</param>
+    /// <param name="cancellationToken">A <see cref="CancellationToken"/> used to cancel the API call.</param>
+    /// <typeparam name="T"></typeparam>
+    /// <returns></returns>
+    IAsyncEnumerable<NatsMsg<T>> GetBatchDirectAsync<T>(StreamMsgBatchGetRequest request, INatsDeserialize<T>? serializer = default, CancellationToken cancellationToken = default);
+
     ValueTask<StreamMsgGetResponse> GetAsync(StreamMsgGetRequest request, CancellationToken cancellationToken = default);
 }

src/NATS.Client.JetStream/Models/StreamMsgBatchGetRequest.cs

@@ -0,0 +1,80 @@
+using System.ComponentModel.DataAnnotations;
+using System.Text.Json.Serialization;
+
+namespace NATS.Client.JetStream.Models;
+
+/// <summary>
+/// A request to the JetStream $JS.API.STREAM.MSG.GET API
+/// </summary>
+public record StreamMsgBatchGetRequest
+{
+    /// <summary>
+    /// The maximum amount of messages to be returned for this request
+    /// </summary>
+    [JsonPropertyName("batch")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    [Range(-1, int.MaxValue)]
+    public int Batch { get; set; }
+
+    /// <summary>
+    /// The maximum amount of returned bytes for this request.
+    /// </summary>
+    [JsonPropertyName("max_bytes")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    [Range(-1, int.MaxValue)]
+    public int MaxBytes { get; set; }
+
+    /// <summary>
+    /// The minimum sequence for returned message
+    /// </summary>
+    [JsonPropertyName("seq")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    [Range(ulong.MinValue, ulong.MaxValue)]
+    public ulong MinSequence { get; set; }
+
+    /// <summary>
+    /// The minimum start time for returned message
+    /// </summary>
+    [JsonPropertyName("start_time")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    [Range(ulong.MinValue, ulong.MaxValue)]
+    public DateTime StartTime { get; set; }
+
+    /// <summary>
+    /// The subject used filter messages that should be returned
+    /// </summary>
+    [JsonPropertyName("next_by_subj")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    [Required]
+#if NET6_0
+    public string Subject { get; set; } = default!;
+#else
+#pragma warning disable SA1206
+    public required string Subject { get; set; }
+
+#pragma warning restore SA1206
+#endif
+
+    /// <summary>
+    /// Return last messages mathing the subjects
+    /// </summary>
+    [JsonPropertyName("multi_last")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    [Range(ulong.MinValue, ulong.MaxValue)]
+    public string[] LastBySubjects { get; set; } = [];
+
+    /// <summary>
+    /// Return message after sequence
+    /// </summary>
+    [JsonPropertyName("up_to_seq")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    [Range(ulong.MinValue, ulong.MaxValue)]
+    public ulong UpToSequence { get; set; }
+
+    /// <summary>
+    /// Return message after time
+    /// </summary>
+    [JsonPropertyName("up_to_time")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
+    public DateTimeOffset UpToTime { get; set; }
+}