Merge pull request #29018 from yyyisyyy11:project4_Lunhan_Yan

dnn: add DynamicQuantizeLinear ONNX layer support #29018

### Pull Request Readiness Checklist

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and target platform(s)
- [x] There is an accuracy test
- [ ] There is a performance test

### Description

Implements the ONNX `DynamicQuantizeLinear` operator (opset 11) for the OpenCV DNN module.

**What it does:**

- Adds `QuantizeDynamicLayer` and `DequantizeDynamicLayer` layer classes
- Registers layers and adds ONNX importer dispatch for `DynamicQuantizeLinear`
- Computes scale and zero-point at runtime from activation min/max
- Quantizes FP32 input to int8 (stored as uint8 - 128, matching OpenCV convention)

**Framework limitation & workaround:**
Due to the single-dtype-per-layer constraint in `LayerData::dtype` (see #29017), the float32 scale output cannot be passed through the CV_8S blob pipeline directly. As a workaround, the scale is encoded as 4 raw bytes in a CV_8S `{1,4}` blob using `memcpy`, and decoded by the downstream `DequantizeDynamic` layer.

**Testing:**

- Custom accuracy tests reproduce all 3 ONNX conformance test cases: `test_dynamicquantizelinear`, `test_dynamicquantizelinear_max_adjusted`, `test_dynamicquantizelinear_min_adjusted`
- Each test verifies: quantized values, scale, zero point, and round-trip dequantize accuracy
- All existing quantization regression tests pass (42/42)

**Conformance tests:**
The 6 conformance tests for `DynamicQuantizeLinear` remain in the parser denylist (they were already denylisted before this PR) because the framework cannot produce mixed-type outputs. The custom tests provide equivalent coverage.

### Files changed

- `modules/dnn/include/opencv2/dnn/all_layers.hpp` — layer class declarations
- `modules/dnn/src/init.cpp` — layer registration
- `modules/dnn/src/onnx/onnx_importer.cpp` — ONNX import dispatch
- `modules/dnn/src/int8layers/quantization_utils.cpp` — layer implementations
- `modules/dnn/test/test_onnx_importer.cpp` — custom accuracy tests

modules/dnn/src/init.cpp

@@ -205,6 +205,8 @@ void initializeLayerFactory()
     CV_DNN_REGISTER_LAYER_CLASS(Quantize,         QuantizeLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Dequantize,       DequantizeLayer);
     CV_DNN_REGISTER_LAYER_CLASS(Requantize,       RequantizeLayer);
+    CV_DNN_REGISTER_LAYER_CLASS(QuantizeDynamic,  QuantizeDynamicLayer);
+    CV_DNN_REGISTER_LAYER_CLASS(DequantizeDynamic, DequantizeDynamicLayer);
     CV_DNN_REGISTER_LAYER_CLASS(ConvolutionInt8,  ConvolutionLayerInt8);
     CV_DNN_REGISTER_LAYER_CLASS(InnerProductInt8, InnerProductLayerInt8);
     CV_DNN_REGISTER_LAYER_CLASS(PoolingInt8,      PoolingLayerInt8);