Add run-level discriminator to container names

[clkao]

Summary

• Injects a 6-char hash of run_id into container names so parallel benchmark runs for the same tasks get unique Docker containers
• Prevents container name collisions when multiple runs execute the same task concurrently

Test plan

• Run two concurrent benchmark runs with overlapping tasks and verify no container name conflicts
• Verify single runs still work correctly with the discriminator in container names

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