[Minor] fix: do not requantize the scales in FP8 scale sweep calibration

[Fridah-nv]

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Summary by CodeRabbit

Release Notes

• New Features

  • Added conditional pre-quantization optimization for static block quantization when scale sweep is enabled.
  • Enhanced calibration flow with configurable scale quantization behavior based on optimization settings.

• Improvements

  • Updated quantization calibration documentation to clarify scale behavior and optimization interactions.

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📝 Walkthrough

Walkthrough

These changes implement an optimized FP8 quantization path for NVFP4 static per-block quantization. When fp8_scale_sweep is enabled, the quantizer skips dynamic FP8 scale quantization by setting a flag that propagates through the calibrator and into the fake quantization path, using pre-computed scales instead.

Changes

Cohort / File(s)	Summary
FP8 scale sweep configuration modelopt/torch/quantization/model_calib.py	Added conditional logic to enable pre-quantization optimization for NVFP4 static per-block quantization when fp8_scale_sweep is enabled; sets skip_fp8_scale_quant flag on the quantizer before MSE calibrator construction. Updated docstring to clarify FP8 scale value count (128 → 126 valid values).
Fake quantization flag handling modelopt/torch/quantization/nn/modules/tensor_quantizer.py	Introduced skip_scale_quant local variable derived from block_sizes["skip_fp8_scale_quant"] in the 2-bit static block quantization path; passes this flag to static_blockwise_fp4_fake_quant instead of always using False.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title accurately describes the main change: preventing scale requantization in FP8 scale sweep calibration, which is the core objective evident in both modified files.

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✨ Finishing touches

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• Commit unit tests in branch fridah/fix-fp8-sweep

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.44%. Comparing base (2a46753) to head (aee1bd7).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
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  Coverage   73.44%   73.44%           
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  Files         194      194           
  Lines       20034    20034           
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  Hits        14714    14714           
  Misses       5320     5320           

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[realAsma]

@Fridah-nv can you please add [Minor] tag in the PR title?

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[Fridah-nv]

Fix applied in #849