The vertex buffer slot is hardcoded to 0 in `VulkanRenderPass.drawMultipleIndexed()`

VulkanRenderPass.drawMultipleIndexed() calls this.setVertexBuffer(0, draw.vertexBuffer().slice()); in VulkanRenderPass.java#304 instead of setVertexBuffer(draw.slot(), draw.vertexBuffer().slice()). The slot field is a first-class member of RenderPass.Draw, used correctly in the GL backend at GlCommandEncoder.java#L449 via renderPass.setVertexBuffer(draw.slot(), ...). On Vulkan, setVertexBuffer maps directly to vkCmdBindVertexBuffers with slot as firstBinding, so the slot value is meaningful. Any draw using slot != 0 will silently bind its vertex buffer to slot 0 instead, reading from the wrong buffer and producing corrupted geometry. All current vanilla Draw instances use slot=0, masking the issue entirely.