MFU tracking for inference

[tdene]

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[tdene]

/claude review

[claude]

Two inline comments:

1. Potential ZeroDivisionError in training.py: total_tps and e2e_tps don't guard against elapsed_time_per_iteration == 0, unlike the neighboring train_tps / inf_tps lines.

2. Missing d_conv in from_args(): InferenceFLOPsConfig.d_conv is used in the conv1d FLOPs term but from_args never reads it from args, silently using the default of 4.

Also noting: none of the new modules (inference_flops.py, gpu_peak_flops.py, mfu_tracker.py) have unit tests. The pure-computation logic in InferenceFLOPsCalculator and MFUTracker would be straightforward to test and would catch regressions in the FLOPs formulas.