Mesh Draw
data class MeshDraw(val vertexSlice: GpuBufferSlice, val indexSlice: GpuBufferSlice, val vertexFormat: VertexFormat, val indexType: VertexFormat.IndexType, val indexCount: Int) : Record
GPU-ready draw descriptor produced from MeshData.
It stores uploaded vertex/index slices plus the draw parameters needed by RenderPass.bindAndDraw.