bench: add M2 Max 38-core GPU roofline

[Jeff271828]

Adds ANE roofline datapoint for Apple M2 Max, 38-core GPU.
Refs #137

Machine: Apple M2 Max Mac14,6
Power: AC + High Power

[sbryngelson]

Thanks for the first M2 Max datapoint! The run looks clean: current main, no local edits, AC + High Power, and all four perf steps reported.

The one failing check was "rooflines table in sync": bench/results/rooflines.json also needs regenerating, and our submission README's git add line forgot to mention it, so that's on us. I pushed the regenerated file to your branch (f64e790) and will merge once CI is green.

Side note for #137: 8.4 GB/s on macOS 26.7.1 makes it less likely that macOS 26 alone explains the very low bandwidth on the M2 Pro (0.98) and M1 MacBook Pro (0.85) rows.