Merge pull request #29577 from abhishek-gola:scan_layer

Add Scan layer to the new engine #29577

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [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 related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/test/test_onnx_conformance_layer_filter__openvino.inl.hpp

@@ -2423,8 +2423,12 @@ CASE(test_rms_normalization_4d_axis_negative_4_expanded)
     SKIP;
 CASE(test_rms_normalization_default_axis_expanded)
     SKIP;
+CASE(test_scan9_multi_state)
+    SKIP;
+CASE(test_scan9_scalar)
+    SKIP;
 CASE(test_scan9_sum)
-    // no filter
+    SKIP;
 CASE(test_scan_sum)
     // no filter
 CASE(test_scatter_elements_with_axis)

modules/dnn/test/test_onnx_conformance_layer_filter_opencv_classic_denylist.inl.hpp

@@ -736,6 +736,9 @@
 "test_reduce_sum_square_empty_set_expanded",
 "test_reduce_log_sum_exp_empty_set_expanded",
 "test_loop11",
+"test_scan9_multi_state",  // Scan supported only by the new graph engine
+"test_scan9_scalar",       // ---- same as above ---
+"test_scan9_sum",          // ---- same as above ---
 "test_eyelike_populate_off_main_diagonal",
 "test_eyelike_with_dtype",
 "test_eyelike_without_dtype",

modules/dnn/test/test_onnx_conformance_layer_parser_denylist.inl.hpp

@@ -272,8 +272,8 @@
 "test_reversesequence_batch",  // Issue:: Parser: Can't create layer "onnx_node_output_0!y" of type "ReverseSequence" in function 'getLayerInstance'
 "test_reversesequence_time",  // ---- same as above ---
 "test_rnn_seq_length",  // Issue:: Parser:  Can't create layer "onnx_node_output_1!Y_h" of type "RNN" in function 'getLayerInstance'
-"test_scan9_sum",  // Issue:: Parser: 'Graph' is not supported in function 'getLayerParams'
-"test_scan_sum", // ---- same as above ---
+// Scan edge cases beyond the opset-9+ dataflow the new engine supports:
+"test_scan_sum",  // opset-8 Scan (leading batch dim + sequence_lens, different semantics)
 "test_sequence_insert_at_back",  // Issue:: Parser:  typeProto.has_tensor_type() in function 'populateNet'
 "test_sequence_insert_at_front",  // ---- same as above ---
 "test_sequence_map_add_1_sequence_1_tensor",
@@ -420,9 +420,6 @@
 "test_linear_attention_no_past_explicit_zeros_expanded",
 "test_linear_attention_prefill_with_past",
 "test_linear_attention_prefill_with_past_expanded",
-// Scan op not supported
-"test_scan9_multi_state",
-"test_scan9_scalar",
 // misc unsupported (expanded subgraphs / new ops)
 "test_castlike_no_saturate_FLOAT_to_FLOAT8E4M3FNUZ_expanded",
 "test_castlike_no_saturate_FLOAT_to_FLOAT8E4M3FN_expanded",