Solve CUDA issues

[muellerzr]

What does this PR do?

#2123 introduced device agnostic testing, but it didn't account for the fact our testing suite relies on never spawning any CUDA processes explicitly until a test is fully called. Replaces all calls to torch.cuda.is_available() with our equivalent check that doesn't rely on touching torch.cuda (and causing issues with the notebook_launcher

Fixes # (issue)

The other failing test on main

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@SunMarc

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[SunMarc]

LGTM !