fix: address review feedback on layerwise detection + header + input validation

- examples/llm_ptq/hf_ptq.py: replace dict-inspection layerwise detection
  with a small recursive helper accepting ModelOptPTQRecipe directly,
  handling list-form QuantizeAlgoCfgType (per coderabbitai, jenchen13).
- examples/llm_ptq/hf_ptq.py: convert recipe-type assert to explicit
  if/raise TypeError so validation is not stripped under python -O
  (per cjluo-nv).
- modelopt_recipes/general/ptq/nvfp4_experts_only-fp8_kv_layerwise.yaml:
  bump new-file copyright header to 2026 per LICENSE_HEADER (per cjluo-nv).

Signed-off-by: realAsma <akuriparambi@nvidia.com>

Author: realAsma

examples/llm_ptq/hf_ptq.py

@@ -960,12 +960,19 @@ def quantize_main(
     if args.recipe is not None and not args.auto_quantize_bits:
         print(f"Use recipe {args.recipe} for quantization")
         recipe = load_recipe(args.recipe)
-        assert isinstance(recipe, ModelOptPTQRecipe), (
-            f"Expected PTQ recipe, but got {type(recipe).__name__} from {args.recipe}"
-        )
+        if not isinstance(recipe, ModelOptPTQRecipe):
+            raise TypeError(
+                f"Expected PTQ recipe, but got {type(recipe).__name__} from {args.recipe}"
+            )
+
+    def _is_layerwise(obj):
+        if isinstance(obj, ModelOptPTQRecipe):
+            return _is_layerwise(obj.quantize.algorithm)
+        if isinstance(obj, list):
+            return any(_is_layerwise(a) for a in obj)
+        return bool(getattr(obj, "layerwise", False))
 
-    recipe_algorithm = recipe.quantize.model_dump().get("algorithm") if recipe else None
-    is_layerwise = isinstance(recipe_algorithm, dict) and recipe_algorithm.get("layerwise", False)
+    is_layerwise = _is_layerwise(recipe)
 
     if args.batch_size == 0:
         # For VL models with image-text calibration, skip automatic batch size detection

modelopt_recipes/general/ptq/nvfp4_experts_only-fp8_kv_layerwise.yaml

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright (c) 2024 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 #
 # Licensed under the Apache License, Version 2.0 (the "License");