Merge pull request #28957 from abhishek-gola:fusion_block_layout_extension

Extend attention fusion for runtime QK scale and add MatMul to Gemm rewriter #28957

### 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_graph_simplifier.cpp

@@ -153,7 +153,10 @@ TEST_F(Test_Graph_Simplifier, BiasedMatMulSubgraph) {
     /* Test for 1 subgraphs
         - BiasedMatMulSubgraph
     */
-    test("biased_matmul", "MatMul");
+    auto engine_forced = static_cast<cv::dnn::EngineType>(
+        cv::utils::getConfigurationParameterSizeT("OPENCV_FORCE_DNN_ENGINE", cv::dnn::ENGINE_AUTO));
+    const std::string expected = engine_forced == cv::dnn::ENGINE_CLASSIC ? "MatMul" : "Gemm";
+    test("biased_matmul", expected);
 }
 
 }}