feat: first take of adding caching support

src/AnthropicClient/Models/Usage.cs

@@ -18,4 +18,16 @@ public class Usage
   /// </summary>
   [JsonPropertyName("output_tokens")]
   public int OutputTokens { get; init; }
+
+  /// <summary>
+  /// Gets the number of tokens written to the cache when creating a new entry
+  /// </summary>
+  [JsonPropertyName("cache_creation_input_tokens")]
+  public int CacheCreationInputTokens { get; init; }
+
+  /// <summary>
+  /// Gets the number of tokens retrieved from the cache for the request.
+  /// </summary>
+  [JsonPropertyName("cache_read_input_tokens")]
+  public int CacheReadInputTokens { get; init; }
 }