214: Rewrite GpuFuture to avoid blocking and to use less space r=kvark a=lachlansneff
Since `GpuFuture` doesn't blocking wait for the mapping to resolve anymore, we need to poll the device for it to actually work. ~~I haven't added that to the `hello-compute` example, so it doesn't work anymore.~~
Co-authored-by: Lachlan Sneff <lachlan.sneff@gmail.com>