Rename Cultures class to MultiCulture throughout codebase

Refactored all references from Cultures to MultiCulture in controllers and base classes. Updated the class definition in MultiCulture.cs to improve clarity and consistency in culture-related functionality. No functional changes were made.

EnvelopeGenerator.Web/Controllers/ViewControllerBase.cs

@@ -8,10 +8,10 @@ namespace EnvelopeGenerator.Web.Controllers;
 public class ViewControllerBase : Controller
 {
     protected readonly ILogger _logger;
-    protected readonly Cultures _cultures;
+    protected readonly MultiCulture _cultures;
     protected readonly IStringLocalizer<Resource> _localizer;
 
-    public ViewControllerBase(ILogger logger, Cultures cultures, IStringLocalizer<Resource> localizer)
+    public ViewControllerBase(ILogger logger, MultiCulture cultures, IStringLocalizer<Resource> localizer)
     {
         _logger = logger;
         _cultures = cultures;