feat: add models for streaming messages

src/AnthropicClient/Models/AnthropicEvent.cs

@@ -0,0 +1,20 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+public record AnthropicEvent
+{
+  public string Type { get; init; } = string.Empty;
+  public EventData Data { get; init; } = default!;
+
+  [JsonConstructor]
+  internal AnthropicEvent()
+  {
+  }
+
+  public AnthropicEvent(string type, EventData data)
+  {
+    Type = type;
+    Data = data;
+  }
+}