Refactor service provider usage and clean up context

Updated `InitializeServicesAndSetMockApplication` to use
`serviceProvider` for setting the Maui context. Removed
unnecessary `using` directive and `AnimationManager`
property from `HandlersContextStub`, indicating a
refactor of animation management functionality.

Author: VladislavAntonyuk

src/CommunityToolkit.Maui.UnitTests/BaseHandlerTest.cs

@@ -72,7 +72,7 @@ static void InitializeServicesAndSetMockApplication(out IServiceProvider service
 		IPlatformApplication.Current = application;
 
 		application.Handler = new ApplicationHandlerStub();
-		application.Handler.SetMauiContext(new HandlersContextStub(mauiApp.Services));
+		application.Handler.SetMauiContext(new HandlersContextStub(serviceProvider));
 
 		CreateElementHandler<MockPopupHandler>(mockPopup);
 		CreateViewHandler<MockPageHandler>(page);

src/CommunityToolkit.Maui.UnitTests/Mocks/HandlersContextStub.cs

@@ -1,19 +1,14 @@
-using Microsoft.Maui.Animations;
-
-namespace CommunityToolkit.Maui.UnitTests.Mocks;
+namespace CommunityToolkit.Maui.UnitTests.Mocks;
 
 class HandlersContextStub : IMauiContext
 {
 	public HandlersContextStub(IServiceProvider services)
 	{
 		Services = services;
 		Handlers = Services.GetRequiredService<IMauiHandlersFactory>();
-		AnimationManager = services.GetService<IAnimationManager>() ?? throw new NullReferenceException();
 	}
 
 	public IServiceProvider Services { get; }
 
 	public IMauiHandlersFactory Handlers { get; }
-
-	public IAnimationManager AnimationManager { get; }
 }