feat: add models for streaming messages

src/AnthropicClient/Models/JsonDelta.cs

@@ -0,0 +1,19 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+public class JsonDelta : ContentDelta
+{
+  [JsonPropertyName("partial_json")]
+  public string PartialJson { get; init; } = string.Empty;
+
+  [JsonConstructor]
+  internal JsonDelta() : base(ContentDeltaType.JsonDelta)
+  {
+  }
+
+  public JsonDelta(string partialJson) : base(ContentDeltaType.JsonDelta)
+  {
+    PartialJson = partialJson;
+  }
+}