Merge pull request #27379 from cudawarped:fix_cuda_convertTo

cuda: Fix GpuMat::convertTo issues described in 27373 #27379

Fix https://github.com/opencv/opencv/issues/27373.

1. `GpuMat::convertTo` uses `convertToScale` due to incorrect overload.
2. There are no runtime checks to prevent the use of `CV_16U` data types in Release builds.

### 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/core/src/cuda/gpu_mat.cu

@@ -546,7 +546,7 @@ void cv::cuda::GpuMat::convertTo(OutputArray _dst, int rtype, Stream& stream) co
         return;
     }
 
-    CV_DbgAssert( sdepth <= CV_64F && ddepth <= CV_64F );
+    CV_Assert( sdepth <= CV_64F && ddepth <= CV_64F );
 
     GpuMat src = *this;
 
@@ -578,6 +578,8 @@ void cv::cuda::GpuMat::convertTo(OutputArray _dst, int rtype, double alpha, doub
     const int sdepth = depth();
     const int ddepth = CV_MAT_DEPTH(rtype);
 
+    CV_Assert(sdepth <= CV_64F && ddepth <= CV_64F);
+
     GpuMat src = *this;
 
     _dst.create(size(), rtype);