Refactor application structure and add unit tests

Added:
- New `ProgressService` class for managing progress indicators.
- New `AssetDatabase`, `AssetOpenHandlerAttribute`, and `AsyncAssetOpenHandlerAttribute` classes for asset handling.
- `Ghost.UnitTest` project for unit testing with associated files and configurations.

Changed:
- `ActivationHandler` class to ensure correct handling of `LaunchActivatedEventArgs`.
- `App.xaml.cs` to register `INotificationService` and `IProgressService`, replacing `StackedNotificationService`.
- `OnLaunched` method in `App.xaml.cs` to correctly call `ActivationHandler.Handle(args)` and start the host.
- `INavigationAware` interface from internal to public for broader access.
- `EditorState.cs` to activate `EditorApplication` with the current service provider.
- Property names in `AssetItem` and `ExplorerItem` structs to `Name` and `FullName`.
- `NotificationService` class to implement `INotificationService` and refactor notification handling.
- `AssetPathToGlyphConverter` to handle file extensions consistently.
- Bindings in `ProjectPage.xaml` and `ProjectPage.xaml.cs` to use `FullName` instead of `Path`.
- `EngineEditorWindow` and `LandingWindow` classes to utilize new notification and progress services.
- `Logger` class to include a new method for logging errors with exceptions.

Updated:
- Manifest files and project files to reflect new structure and dependencies.
- Solution file `GhostEngine.sln` to include the new unit test project.
- Added several new test classes and methods in `UnitTests.cs`.

Ghost.Editor/SceneGraph/EditorWorldManager.cs

@@ -0,0 +1,53 @@
+using Ghost.Editor.Resources;
+using Ghost.Editor.Services.Contracts;
+using Ghost.Engine.Resources;
+using System.Text.Json;
+
+namespace Ghost.Editor.SceneGraph;
+
+public enum OpenWorldMode
+{
+    Single,
+    Additive,
+    AdditiveWithoutLoading
+}
+
+public static class EditorWorldManager
+{
+    // TODO: Use guid keys instead of string paths for better performance and uniqueness
+    private static readonly Dictionary<string, WorldNode> _loadedWorlds = new();
+    public static IEnumerable<WorldNode> LoadedWorlds => _loadedWorlds.Values;
+
+    public static event Action<WorldNode>? OnWorldLoaded;
+    public static event Action<WorldNode>? OnWorldUnloaded;
+
+    public static async Task LoadWorld(string worldPath)
+    {
+        if (_loadedWorlds.ContainsKey(worldPath)
+            || !File.Exists(worldPath)
+            || Path.GetExtension(worldPath) != FileExtensions.SCENE_FILE_EXTENSION)
+        {
+            return;
+        }
+
+        var progressService = EditorApplication.GetService<IProgressService>();
+        progressService.ShowIndeterminateProgress("Loading world...");
+
+        foreach (var world in _loadedWorlds)
+        {
+            world.Value.Unload();
+            OnWorldUnloaded?.Invoke(world.Value);
+        }
+
+        await using var readStream = new FileStream(worldPath, FileMode.Open, FileAccess.Read, FileShare.Read);
+        var deserializedScene = await JsonSerializer.DeserializeAsync<WorldNode>(readStream, StaticResource.defaultSerializerOptions) ?? throw new Exception("Deserialization failed.");
+
+        _loadedWorlds.Clear();
+
+        _loadedWorlds[worldPath] = deserializedScene;
+        await deserializedScene.LoadAsync();
+
+        progressService.HideProgress();
+        OnWorldLoaded?.Invoke(deserializedScene);
+    }
+}