Refactor asset streaming & resource management system

- Introduce Ghost.Engine.Streaming namespace and split asset entry logic into type-specific classes (TextureAssetEntry, MeshAssetEntry, SceneAssetEntry)
- Make AssetEntry abstract; add AssetEntryFactory for type dispatch
- Update AssetManager and ResourceStreamingProcessor for new entry model, supporting uploadable and processable assets
- Redesign scene/mesh asset loading, serialization, and binary formats with versioning (SceneContentHeader, MeshContentHeader)
- Move SceneLoadingType to Ghost.Engine and make public
- Inline performance-critical APIs with MethodImplOptions.AggressiveInlining
- Add deep cloning and improved resource management for Mesh and meshlet data
- Allow nullable log messages in Logger
- Update Misaki.HighPerformance package references
- Remove obsolete files (Asset.cs, ActivationHandler.cs, old mesh logic)
- Improve resource release logic in ResourceManager
- Update RenderContext and ResourceStreamingContext for new streaming model
- Add UnsafeArray/UnsafeList clone utilities
- Update scene serialization/deserialization for new format
- Update tests for new APIs, asset states, and formats

src/Editor/Ghost.Editor/Models/ExplorerItem.cs

@@ -1,6 +1,5 @@
 using CommunityToolkit.Mvvm.ComponentModel;
-using Ghost.Core.Utilities;
-using Ghost.Engine;
+using Ghost.Engine.Streaming;
 using System.Collections.ObjectModel;
 
 namespace Ghost.Editor.Models;