Increase CG cover from max_requests to max_tokens

[tdene]

What does this PR do ?

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[tdene]

/ok to test 830754b

[tdene]

/claude review

[claude]

LGTM

[sidsingh-nvidia]

I am torn on if cuda-graphing everything should be opt-in/default/only-thing. This PR makes it the only-thing.

[tdene]

I am torn on if cuda-graphing everything should be opt-in/default/only-thing. This PR makes it the only-thing.

If the user does not request CUDA graphs, nothing is graphed. If the user does request CUDA graphed, prior to this PR only some of the steps are graphed, while after this PR everything is graphed.

The only downside I see is the memory consumption of the biggest recorded CUDA graph. But that is already memory consumption that would have to be paid for an eager batch of that size (due to activations). If the user wants to limit their memory consumption they need to specify max_tokens anyway or they might OOM during eager steps. CUDA graphing everything makes it so that the OOM can only happen up-front, instead of unpredictably in the middle of the step.

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25771832280

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25776760461

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/25782610816