multigpuswapchain: wait for GPU idle before deleting Vulkan swapchain
deleteResources() resets the Vulkan swapchain and destroys the image allocations on the CPU without waiting for the GPU to finish execution. If the Copy Engine is actively writing to these buffers in the background, the driver unmaps the page tables, triggering write page faults (Xid 31). Fix this by calling waitIdle() on the Vulkan device before deallocation.