fix(cuda_graphs): handle TE 2.15 removal of FP8GlobalStateManager.set_skip_fp8_weight_update_tensor

[balasaajay]

What does this PR do ?

Fixes - #4707

After the CI base image bumped to TE 2.15, every FP8-enabled cudagraph runner construction crashed with:
AttributeError: type object 'FP8GlobalStateManager' has no attribute 'set_skip_fp8_weight_update_tensor'

Route the three calls in cuda_graphs.py through a new helper _set_skip_fp8_weight_update_tensor(skip) that:

• on TE ≤ 2.14: calls the legacy classmethod (unchanged behavior).
• on TE ≥ 2.15: writes FP8GlobalStateManager.quantization_state.skip_fp8_weight_update_tensor directly, lazily allocating the persistent 1-element float32 CUDA tensor and updating it in place via fill_(skip) — preserving the data pointer that captured cudagraphs read from, so the flag can still be toggled between microbatches without re-capturing.
  No behavior change on supported TE versions; unblocks CI on TE ≥ 2.15.

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[balasaajay]

/ok to test a0cd6d7

[balasaajay]

/ok to test 5a661e2

[balasaajay]

/ok to test a94a352

[svcnvidia-nemo-ci]

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/26301573343