Run Thrust unit tests with `__half`

[brycelelbach]

It seems we do not do this. It'd probably be a good idea. We could potentially add it to one of the list of tests types - maybe removing another type to make room for it. __half is a nice thing to test because it's numeric-like but not a builtin type.

[alliepiper]

Agreed. Just to note, I ran into issues trying to benchmark with __half, seems the thrust rng facilities don't support it. There may be quite a bit of infrastructure work involved in making this happen.