Merge pull request #28588 from abhishek-gola:ORT_GPU_wrapper

Added OnnxRuntime GPU wrapper #28588

### 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/include/opencv2/dnn/dnn.hpp

@@ -765,6 +765,19 @@ CV__DNN_INLINE_NS_BEGIN
          */
         CV_WRAP void setPreferableTarget(int targetId);
 
+        /** @brief Finalizes the network configuration and prepares it for inference.
+         *
+         * This method must be called after setting backend/target via
+         * setPreferableBackend() and setPreferableTarget(), and before the first
+         * forward() call. It creates the underlying execution session (e.g. ONNX
+         * Runtime session) on the configured backend/target. If not called
+         * explicitly, the first forward() will call it automatically.
+         *
+         * Calling finalizeNet() early lets you pay the one-time setup cost at a
+         * predictable point and catch configuration errors before inference.
+         */
+        CV_WRAP void finalizeNet();
+
         /**
          * @brief Set the tracing mode
          * @param[in] tracingMode the tracing mode, see DNN_TRACE_*