Refactor: standardize namespace and using directive style

Refactored all C# test files to use explicit namespace declarations and moved all using directives inside the namespace block for consistency. Updated assembly info and cache files to reflect the new build. Adjusted MvcTestingAppManifest.json to use fully qualified assembly names. No functional changes; all updates are related to code style, organization, and project metadata.

tests/Jellyfin.Api.Tests/Controllers/UserControllerTests.cs

@@ -2,6 +2,8 @@
 // Copyright (c) PlaceholderCompany. All rights reserved.
 // </copyright>
 
+namespace Jellyfin.Api.Tests.Controllers;
+
 using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
@@ -25,8 +27,6 @@ using Moq;
 using Nikse.SubtitleEdit.Core.Common;
 using Xunit;
 
-namespace Jellyfin.Api.Tests.Controllers;
-
 public class UserControllerTests
 {
     private readonly UserController _subject;