feat: add DeleteMessageBatchAsync method and MessageBatchDeleteResponse model with tests

src/AnthropicClient/Models/MessageBatchDeleteResponse.cs

@@ -0,0 +1,17 @@
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents a message batch delete response.
+/// </summary>
+public class MessageBatchDeleteResponse
+{
+  /// <summary>
+  /// Gets the ID of the message batch that was deleted.
+  /// </summary>
+  public string Id { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Gets the type of the message batch response.
+  /// </summary>
+  public string Type { get; init; } = string.Empty;
+}