Improve speed in combining per-channel data (#21563)

### Description
<!-- Describe your changes. -->
Improve speed in combining `per-channel` data for using a single
`np.concatenate` instead of multiple `np.concatenates` within a for
loop.

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

Fix the issue https://github.com/microsoft/onnxruntime/issues/21562

Signed-off-by: duansheng.liu <44742794+duanshengliu@users.noreply.github.com>

onnxruntime/python/tools/quantization/base_quantizer.py

@@ -418,6 +418,9 @@ class BaseQuantizer:
         zero_point_list = []
         scale_list = []
         quantized_per_channel_data_list = []
+        weights_shape = list(weights.shape)
+        reshape_dims = list(weights_shape)  # deep copy
+        reshape_dims[channel_axis] = 1  # only one per channel for reshape
         for i in range(channel_count):
             per_channel_data = weights.take(i, channel_axis)
             channel_override_index = i if i < num_channel_overrides else 0
@@ -460,17 +463,10 @@ class BaseQuantizer:
 
             zero_point_list.append(zero_point)
             scale_list.append(scale)
-            quantized_per_channel_data_list.append(quantized_per_channel_data)
+            quantized_per_channel_data_list.append(np.asarray(quantized_per_channel_data).reshape(reshape_dims))
 
         # combine per_channel_data into one
-        weights_shape = list(weights.shape)
-        reshape_dims = list(weights_shape)  # deep copy
-        reshape_dims[channel_axis] = 1  # only one per channel for reshape
-        quantized_weights = np.asarray(quantized_per_channel_data_list[0]).reshape(reshape_dims)
-        for i in range(1, len(quantized_per_channel_data_list)):
-            channel_weights = np.asarray(quantized_per_channel_data_list[i]).reshape(reshape_dims)
-            quantized_weights = np.concatenate((quantized_weights, channel_weights), channel_axis)
-
+        quantized_weights = np.concatenate(quantized_per_channel_data_list, channel_axis)
         q_weight_name = weight_name + TENSOR_NAME_QUANT_SUFFIX
         zp_name = weight_name + "_zero_point"
         scale_name = weight_name + "_scale"