…-buffer-stride-variable

Move GpuMat initialization to a more suitable scope.

…espace_for_cuda_13.2

Use different namespace for cuda 13.2#4097

### Pull Request Readiness Checklist

Hi Alexander, you mentioned we should define the namespace in CMake and keep the original namespace but after reviewing the new CUDA 13.2 namespaces with coworker @daniel-mitchell-tt, we think the new namespace should be used to replace old namespace.

CUDA 13.2 namespace:
/usr/local/cuda-13.2/targets/sbsa-linux/include/cccl/cuda/std/__internal/namespaces.h:45:#  define _CCCL_BEGIN_NAMESPACE_CUDA_STD _LIBCUDACXX_PROLOGUE_INCLUDE_CHECK() namespace cuda::std { inline namespace _LIBCUDACXX_ABI_NAMESPACE {

CUDA 12.6 namespace:
/usr/local/cuda-12.6/targets/x86_64-linux/include/cuda/std/detail/libcxx/include/__config:1216:#  define _LIBCUDACXX_BEGIN_NAMESPACE_STD_NOVERSION namespace cuda { namespace std {

Comment Daniel made: opencv#4091 (comment)

Fix: opencv#4091 
Related to: opencv#4095 (closed PR)

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
- [ ] 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

Fixed division zero and unintentional bias in Otsu's threshold (CUDA)

Fixed build warnings in CUDA.

Fix documentation for DisparityFilter disparity map types