[DOCS] Improving code snippets for quantization (#19479)

* improve-snippets

* Apply suggestions from code review

Co-authored-by: Alexander Suslov <alexander.suslov@intel.com>

* Update docs/optimization_guide/nncf/ptq/code/ptq_tensorflow.py

Co-authored-by: Alexander Suslov <alexander.suslov@intel.com>

* update-path

* Update docs/optimization_guide/nncf/ptq/code/ptq_torch.py

---------

Co-authored-by: Alexander Suslov <alexander.suslov@intel.com>

docs/optimization_guide/nncf/ptq/code/ptq_onnx.py

@@ -16,7 +16,8 @@ calibration_dataset = nncf.Dataset(calibration_loader, transform_fn)
 #! [dataset]
 
 #! [quantization]
-model = ... # onnx.ModelProto object
+import onnx
+model = onnx.load("model_path")
 
 quantized_model = nncf.quantize(model, calibration_dataset)
 #! [quantization]

docs/optimization_guide/nncf/ptq/code/ptq_openvino.py

@@ -15,14 +15,13 @@ calibration_dataset = nncf.Dataset(calibration_loader, transform_fn)
 #! [dataset]
 
 #! [quantization]
-model = ... # openvino.runtime.Model object
+import openvino.runtime as ov
+model = ov.Core().read_model("model_path")
 
 quantized_model = nncf.quantize(model, calibration_dataset)
 #! [quantization]
 
 #! [inference]
-import openvino.runtime as ov
-
 # compile the model to transform quantized operations to int8
 model_int8 = ov.compile_model(quantized_model)
 

docs/optimization_guide/nncf/ptq/code/ptq_tensorflow.py

@@ -15,7 +15,8 @@ calibration_dataset = nncf.Dataset(calibration_loader, transform_fn)
 #! [dataset]
 
 #! [quantization]
-model = ... # tensorflow.Module object
+import tensorflow as tf
+model = tf.saved_model.load("model_path")
 
 quantized_model = nncf.quantize(model, calibration_dataset)
 #! [quantization]

docs/optimization_guide/nncf/ptq/code/ptq_torch.py

@@ -15,7 +15,8 @@ calibration_dataset = nncf.Dataset(calibration_loader, transform_fn)
 #! [dataset]
 
 #! [quantization]
-model = ... # torch.nn.Module object
+import torchvision
+model = torchvision.models.resnet50(pretrained=True)
 
 quantized_model = nncf.quantize(model, calibration_dataset)
 #! [quantization]