Works on cuda 12.4 and up. If CUDA doesn't exist, then don't enable
the backend. This is an env var that needs to be set, so it's not really
possible to set it via config.yml.
This used to be experimental, but it's probably fine to keep it enabled
since it only provides a benefit.
Signed-off-by: kingbri <8082010+kingbri1@users.noreply.github.com>
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