fix: remove unnecessary usings

src/AnthropicClient/Models/CreateFileRequest.cs

@@ -1,5 +1,3 @@
-using System.Text.Json.Serialization;
-
 using AnthropicClient.Utils;
 
 namespace AnthropicClient.Models;

src/AnthropicClient/Models/DocumentSource.cs

@@ -1,7 +1,5 @@
 using System.Text.Json.Serialization;
 
-using AnthropicClient.Utils;
-
 namespace AnthropicClient.Models;
 
 /// <summary>

src/AnthropicClient/Models/ImageSource.cs

@@ -1,7 +1,5 @@
 using System.Text.Json.Serialization;
 
-using AnthropicClient.Utils;
-
 namespace AnthropicClient.Models;
 
 /// <summary>