Update base for Update on "Improve QAT nvfp4 numerics"

**Summary:** Similar to #2986,
this commit improves the prepare vs convert SQNR of NVFP4 QAT
from 12 to inf. This is achieved by refactoring NVFP4 QAT to
mimick the PTQ numerics exactly, using a new linear class to
incorporate both the quantization and mm logic.

**Test Plan:**
```
python test/quantization/test_qat.py -k test_qat_nvfp4
python test/quantization/test_qat.py -k test_quantize_api_nvfp4
```

End-to-end tests TBD.

[ghstack-poisoned]

Author: andrewor14