Fix remaining RoutingState constructors to use ImmediateScheduler

- Fixed RoutedViewHostTests.cs (WPF) missing scheduler parameter
- Fixed WinFormsRoutedViewHostTests.cs (3 instances) missing scheduler parameter
- Fixed AdvancedAOTTests.cs missing scheduler parameter
- Ensures all test RoutingState instances execute synchronously preventing async hangs
- All 6,155 tests passing

Author: glennawatson

src/tests/ReactiveUI.AOTTests/AdvancedAOTTests.cs

@@ -28,7 +28,7 @@ public class AdvancedAOTTests
     [Test]
     public async Task RoutingState_Navigation_WorksInAOT()
     {
-        var routingState = new RoutingState();
+        var routingState = new RoutingState(ImmediateScheduler.Instance);
         var viewModel = new TestRoutableViewModel();
 
         // Test navigation

src/tests/ReactiveUI.WinForms.Tests/winforms/WinFormsRoutedViewHostTests.cs

@@ -17,7 +17,7 @@ public class WinFormsRoutedViewHostTests
     public async Task ShouldDisposePreviousView()
     {
         var viewLocator = new FakeViewLocator { LocatorFunc = _ => new FakeWinformsView() };
-        var router = new RoutingState();
+        var router = new RoutingState(ImmediateScheduler.Instance);
         var target = new WinFormsRoutedViewHost { Router = router, ViewLocator = viewLocator };
         router?.Navigate?.Execute(new FakeWinformViewModel());
 
@@ -36,7 +36,7 @@ public async Task ShouldSetDefaultContentWhenViewModelIsNull()
     {
         var defaultContent = new Control();
         var viewLocator = new FakeViewLocator { LocatorFunc = static _ => new FakeWinformsView() };
-        var router = new RoutingState();
+        var router = new RoutingState(ImmediateScheduler.Instance);
         var target = new WinFormsRoutedViewHost
         {
             Router = router,
@@ -51,7 +51,7 @@ public async Task ShouldSetDefaultContentWhenViewModelIsNull()
     public async Task WhenRoutedToViewModelItShouldAddViewToControls()
     {
         var viewLocator = new FakeViewLocator { LocatorFunc = static _ => new FakeWinformsView() };
-        var router = new RoutingState();
+        var router = new RoutingState(ImmediateScheduler.Instance);
         var target = new WinFormsRoutedViewHost { Router = router, ViewLocator = viewLocator };
         router?.Navigate?.Execute(new FakeWinformViewModel());
 

src/tests/ReactiveUI.Wpf.Tests/Xaml/RoutedViewHostTests.cs

@@ -85,7 +85,7 @@ public async Task RoutedViewHostDefaultContentNotNullWithViewModelAndActivated()
     [TestExecutor<WpfWithViewAndRoutingExecutor>]
     public async Task RoutedViewHostDefaultContentNotNullWithViewModelAndNotActivated()
     {
-        var router = new RoutingState();
+        var router = new RoutingState(ImmediateScheduler.Instance);
         var viewModel = new TestViewModel();
 
         var uc = new RoutedViewHost