Add support for TE MXFP8 recipe in accelerate

[pstjohn]

What does this PR do?

Adds support for the MXFP8 format in TE. See the TE docs pages for more background:
https://docs.nvidia.com/deeplearning/transformer-engine/user-guide/examples/fp8_primer.html#MXFP8-and-block-scaling

This adds an additional fp8_recipe argument, use_mxfp8_block_scaling, that switches the recipe from the DelayedScaling recipe to MXFP8BlockScaling.

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[pstjohn]

This is outside the initial scope for this PR, but there's some oddity when using Deepspeed + FP8 + the HF Trainer.

If you set bf16: True in your TrainingArguments, the trainer will override the fp8 parameter you pass to Accelerate (manually setting ACCELERATE_MIXED_PRECISION=bf16) here:

And if you omit it, ACCELERATE_MIXED_PRECISION stays as FP8 but you then get an error raised here about a config mismatch:

ValueError: Please correct the following DeepSpeed config values that mismatch TrainingArguments values:
- ds bf16.enabled=True vs hf bf16|bf16_full_eval=False
The easiest method is to set these DeepSpeed config values to 'auto'.

Interestingly it's still possible to use FP8 with deepspeed currently? But it seems like a bug. This check:
https://github.com/huggingface/accelerate/blame/2f075c724ccb4e38fade64db3b0627ca167b5fd2/src/accelerate/accelerator.py#L2046-L2047
will trigger when you pass an fp8 backend with deepspeed, because it only checks for fp8_backend, not fp8_enabled. But you wont create the TERecipeKwargs object, so it will just create the fp8 autowrap context with the default recipe.

There have been a number of "FP8 + deepspeed" PRs here in the past, I'm wondering if the cleanest option is to separate "mixed_precision" from fp8. fp8 typically uses bf16 for model weights and between FP8-enabled layers anyways.

[pstjohn]

formatting only change, not sure why it's changing it from main

[S1ro1]

Do I understand correctly that this only covers DeepSpeed?