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stitching: pass warp params by value to avoid CUDA constant races #28118 ### 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 the Apache 2 License. - [x] To the best of my knowledge, the proposed patch is not based on 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 are accuracy tests, performance tests, and test data in the opencv_extra repository, if applicable. The patch to opencv_extra uses the same branch name. - [ ] The feature is well documented and sample code can be built with the project CMake configuration. Fixes #26870. In `modules/stitching/src/cuda/build_warp_maps.cu`, the original implementation copied parameters into global GPU constant symbols: ```cpp cudaSafeCall(cudaMemcpyToSymbol(build_warp_maps::ck_rinv, k_rinv, 9 * sizeof(float))); cudaSafeCall(cudaMemcpyToSymbol(build_warp_maps::cr_kinv, r_kinv, 9 * sizeof(float))); cudaSafeCall(cudaMemcpyToSymbol(build_warp_maps::cscale, &scale, sizeof(float))); ``` As discussed in the issue, this can cause race conditions when multiple warps are built concurrently. This patch removes the use of these global constant symbols and instead passes the required data as kernel parameters (a total of 11 floats encapsulated in `WarpParams`). One potential concern is increased register pressure due to additional kernel arguments. However, based on experiments using the test case from issue #26870, there is no significant performance regression; in fact, a small speed‑up was observed. Testing was performed on an NVIDIA GeForce RTX 4090 (single GPU). Note: ./bin/opencv_perf_stitching did not run successfully on my system even with an unmodified git checkout, so performance was evaluated using the test case from issue #26870 instead.
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