[WIP] fix qparams decompression

[shanjiaz]

Updated the decompress_weight function to unpack zero_point/cast scale dtype during decompression. Replace the tensor in module with updated one.

Example script now generates coherent result:

(llm-compressor) [shanjiaz@nma-a100-solo-4-preserve llm-compressor]$ python zp_decompression.py 
`torch_dtype` is deprecated! Use `dtype` instead!
Compressing model: 154it [00:00, 747.12it/s]



========== SAMPLE GENERATION ==============
<s> Hello my name is John and I am a software engineer. I have been working in the tech industry for the past 10 years. I have worked on various projects and have gained a lot of experience. I am passionate about technology and have a keen interest in the latest technologies. I have a bachelor's degree in computer science and have completed several certifications in various technologies. I am currently working as a software engineer at a leading technology company. In my free time, I enjoy
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[dsikka]

Just an fyi: #509
This will also impact mxfp4.
I've turned off mxfp4 decompression in the meantime / lower priority anyway

[dsikka]

Would it be cleaner to add optional:
compress_scale / decompress_scale
and compress_zp / decompress_zp functions?

This would impact:

• PackedCompressor (packed zp)
• NVFP4PackedCompressor (fp8 scales)
• MXFP4PackedCompressor (uint8 scales)

[shanjiaz]

Would it be cleaner to add optional: compress_scale / decompress_scale and compress_zp / decompress_zp functions?

This would impact:

• PackedCompressor (packed zp)
• NVFP4PackedCompressor (fp8 scales)
• MXFP4PackedCompressor (uint8 scales)

Sure! I can do that.