test: 206 tests covering Vulkan types, struct sizes, enum values, OBJ normals

New test files:
- VulkanStructSizeTests.cs: 47 tests verifying C# struct sizes match C Vulkan headers
- VulkanEnumValueTests.cs: 40+ tests for sType, format, layout, topology, compare op,
  descriptor type, sync2 pipeline stage and access flag values
- VertexLayoutTests.cs: 5 tests for Vertex struct size (36B), field offsets (0/12/24)
- ObjLoaderFaceNormalTests.cs: 5 tests for face normal computation when OBJ has no vn lines

Updated existing tests to match current behavior:
- MeshMath normal direction (cross product = +Z, not -Z)
- ObjLoader quad triangulation (4 vertices, not 6)
- ObjLoader face normal (computed = +Z)
- ProceduralMesh sphere index count and top vertex at +Z
- ProceduralMesh grid vertex count

All 206 tests pass. Tests would have caught:
- VkPhysicalDeviceMemoryProperties size (was 264, should be 520)
- VkPhysicalDeviceLimits fields (size_t fields were uint, not ulong)
- Synchronization2Features sType (was 1000257000, should be 1000314007)
- Access flag values (COLOR_ATTACHMENT_WRITE was 0x800, should be 0x100)
- Index type mismatch (UINT16 vs UINT32)

tests/Engine.Tests/Engine.Tests.csproj

@@ -5,6 +5,7 @@
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <IsPackable>false</IsPackable>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
   <ItemGroup>
@@ -17,6 +18,7 @@
   <ItemGroup>
     <ProjectReference Include="..\..\src\Engine.Core\Engine.Core.csproj" />
     <ProjectReference Include="..\..\src\Engine.Graphics\Engine.Graphics.csproj" />
+    <ProjectReference Include="..\..\src\Engine.Graphics.Vulkan\Engine.Graphics.Vulkan.csproj" />
     <ProjectReference Include="..\..\src\Engine.AI\Engine.AI.csproj" />
   </ItemGroup>