feat: implement GetMessageBatchResultsAsync method

src/AnthropicClient/Json/JsonSerializationOptions.cs

@@ -17,6 +17,7 @@ static class JsonSerializationOptions
       new EventDataConverter(),
       new ContentDeltaConverter(),
       new JsonStringEnumConverter(),
+      new MessageBatchResultConverter(),
     },
     DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
   };

src/AnthropicClient/Json/MessageBatchResultConverter.cs

@@ -0,0 +1,29 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+using AnthropicClient.Models;
+
+namespace AnthropicClient.Json;
+
+class MessageBatchResultConverter : JsonConverter<MessageBatchResult>
+{
+  public override MessageBatchResult Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+  {
+    using var jsonDocument = JsonDocument.ParseValue(ref reader);
+    var root = jsonDocument.RootElement;
+    var type = root.GetProperty("type").GetString();
+    return type switch
+    {
+      MessageBatchResultType.Succeeded => JsonSerializer.Deserialize<SucceededMessageBatchResult>(root.GetRawText(), options)!,
+      MessageBatchResultType.Errored => JsonSerializer.Deserialize<ErroredMessageBatchResult>(root.GetRawText(), options)!,
+      MessageBatchResultType.Canceled => JsonSerializer.Deserialize<CanceledMessageBatchResult>(root.GetRawText(), options)!,
+      MessageBatchResultType.Expired => JsonSerializer.Deserialize<ExpiredMessageBatchResult>(root.GetRawText(), options)!,
+      _ => throw new JsonException($"Unknown message batch result type: {type}")
+    };
+  }
+
+  public override void Write(Utf8JsonWriter writer, MessageBatchResult value, JsonSerializerOptions options)
+  {
+    JsonSerializer.Serialize(writer, value, value.GetType(), options);
+  }
+}