Pull Request Readiness Checklist

• I agree to contribute to the project under Apache 2 License.

• 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

• The PR is proposed to the proper branch

• 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.

• The feature is well documented and sample code can be built with the project CMake

• This PR adds ARM64 NEON intrinsics-based implementation for the cvRound function in fast_math.hpp for ARM64 targets (_MSC_VER && _M_ARM64).

• Both float and double overloads now use NEON intrinsics (vcntn_s32_f32, vcvtn_s64_f64, etc.) for efficient and accurate rounding.

• The implementation is consistent with platform-specific handling already present for SSE2 (x64) and does not affect non-ARM64 builds.

Performance Improvements :

• The optimization significantly improves the performance of cvRound on Windows ARM64 targets.
• The table below shows timing comparisons before and after the optimization: