feat: create chat message

src/AnthropicClient/Models/ChatUsage.cs

@@ -0,0 +1,21 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents the usage of a chat response.
+/// </summary>
+public class ChatUsage
+{
+  /// <summary>
+  /// Gets the number of input tokens used.
+  /// </summary>
+  [JsonPropertyName("input_tokens")]
+  public int InputTokens { get; set; }
+
+  /// <summary>
+  /// Gets the number of output tokens used.
+  /// </summary>
+  [JsonPropertyName("output_tokens")]
+  public int OutputTokens { get; set; }
+}