GPU tests for sonar ps

[lars-t-hansen]

This builds on #216. That patch tests sonar sysinfo but we want more, definitely sonar ps.

The way I usually do this manually is run a biggish computation - matrix multiply - and then run sonar ps while that's running, and then look for output that indicates the GPU is in use. At that point we can inspect the GPU field, make sure it looks sane. I have cuda and hip versions of this code and that's probably good enough (and has the fewest dependencies). I could see how it could be hard to automate that, but since it'll be a test that only runs on nodes that we control when we run tests interactively it may be OK.

[lars-t-hansen]

Going to not block 0.13 on this.