feat: add models for streaming messages

src/AnthropicClient/Models/EventData.cs

@@ -0,0 +1,13 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+public abstract class EventData
+{
+  public string Type { get; init; }
+
+  protected EventData(string type)
+  {
+    Type = type;
+  }
+}