feat: render 2 rotating cubes side by side

- Push constant changed from float angle (4B) to mat4 model (64B)
- Two draw calls with different model matrices (x=-1.5 and x=+1.5)
- Both cubes rotate around Y axis at 0.2 rad/s
- 0 validation errors

src/Engine.Graphics.Vulkan/VulkanPipeline.cs

@@ -154,7 +154,7 @@ internal sealed unsafe class VulkanPipeline : IDisposable
             {
                 stageFlags = VkShaderStageFlags.Vertex,
                 offset = 0,
-                size = 4,
+                size = 64,
             };
 
             var descLayout = DescriptorSetLayout;