NVFP4 Emulation

[dsikka]

Summary:

• Add CompressedTensors NVFP4 Emulation Scheme
• Move emulations functionality into shared utilities

ModelOpt Emulation Changes:

• Don't run activations quantization to start --> seemed to be getting gibberish even with it turned off
• Update how the global scale is applied. I think they're storing the inverse? Updating this allows the coherent outputs for the Nvidia 70b checkpoint

Should now support ct models produced and compressed from the following branches:

1. FP4 Weights: [NVFP4][WIP] Add NVFp4 Support compressed-tensors#287
2. Compression: [WIP][NVFP4] Add compression/decompression code compressed-tensors#291
3. LLM Compressor: [NVFP4][WIP]: Add FP4 Support vllm-project/llm-compressor#1309

lm-evals/generations should work with weight only dequant:

lm_eval --model vllm \
    --model_args pretrained=nm-testing/llama2.c-stories110M-FP4,enforce_eager=True \
    --tasks gsm8k \
    --device cuda:0 \
    --batch_size 8

import numpy
import torch

from vllm import LLM, SamplingParams

prompts = ["The Swiss Alps are", "The president of the USA is", "The Boston Bruins are"]

# Create a sampling params object for greedy sampling
sampling_params = SamplingParams(temperature=0.80, top_p=0.95, max_tokens=40, min_tokens=10)
llm  = LLM('nm-testing/llama2.c-stories110M-FP4', enforce_eager=True)


# Print the outputs.
output = llm.generate(prompts, sampling_params)
for o in output:
    print(o.outputs[0].text)
    print("\n")

ToDo:

• Generally activation quant support - still need to understand how the input scales should be applied
• Improve compression speed in compressed-tensors. The current speed is a bottleneck atm

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