Use SLURM singleton dependency for GPU jobs to prevent conflicts

[JRPan]

Summary

• Add srun --job-name=gpu-lock --dependency=singleton --partition=tgrogers-dgx -- wrapper to GPU tracer jobs in main.yml and weekly.yml
• This ensures only one GPU job runs at a time across all CI runners, preventing GPU resource conflicts
• Change Tracer-Tool and Tracer-Weekly jobs to run on tgrogers-raid since GPU work is now submitted via SLURM

Test plan

• Verify CI workflow runs successfully
• Confirm GPU jobs are properly serialized via SLURM singleton dependency

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