Use a single vk.Buffer

[tiawl]

https://vulkan-tutorial.com/en/Vertex_buffers/Index_buffer#page_Using-an-index-buffer specifies

[Driver developers recommend](https://developer.nvidia.com/vulkan-memory-management) that you also store multiple buffers, like the vertex and index buffer, into a single [VkBuffer](https://www.khronos.org/registry/vulkan/specs/1.0/man/html/VkBuffer.html) and use offsets in commands like [vkCmdBindVertexBuffers](https://www.khronos.org/registry/vulkan/specs/1.0/man/html/vkCmdBindVertexBuffers.html). The advantage is that your data is more cache friendly in that case, because it's closer together. It is even possible to reuse the same chunk of memory for multiple resources if they are not used during the same render operations, provided that their data is refreshed, of course. This is known as aliasing and some Vulkan functions have explicit flags to specify that you want to do this.