[EPIC] Third-party testing in CI

We want to make sure we keep important projects that build on top of CCCL working and happy.

The best way for us to do that is to regularly test external projects as part of our CI.

As much as we'd love to make every CCCL user a part of our CI, the maintenance burden would be far too high. So we'll have to be selective about which projects we add. Furthermore, any project we add will need to come with volunteering time and energy to help set it up and keep it running :)

### Tasks
- [x] https://github.com/NVIDIA/cccl/issues/1508
- [x] https://github.com/NVIDIA/cccl/issues/2264