Key changes:
- snapshot_amax_to_cpu(): copies all quantizer _amax to CPU and saves
to disk (~50MB) right after mtq.quantize() returns, before any other
GPU operation can corrupt them
- force_all_amax_to_cpu(): nuclear option, moves _pre_quant_scale and
_global_amax to CPU too
- _FORCE_AMAX_CPU flag + patched amax setter: after calibration, any
future amax writes go to CPU instead of GPU
- --validate-only mode to check saved state without running anything
- restore_amax_from_snapshot() for --export-only recovery
- torch.cuda.empty_cache() + gc.collect() between steps
- Patches: export_amax CPU fallback, get_activation_scaling_factor
clamp instead of assert
- New scripts/quantize_nvfp4.py: runs full ModelOpt pipeline in-process
- Saves calibrated state after calibration (insurance against export crashes)
- Patches modelopt for V4: ModuleList quantizers, stale GPU tensor safety
- --export-only flag to retry export from saved calibration state
- Removed old model_opt_nvfp4_full.py (shell wrapper)
- Updated README with new pipeline docs and bug #5/#6
