CI: VS2026

[ptheywood]

Use windows-2025 for CUDA >= 13.2 to use Visual Studio 2026

Also updates the readme to mention 2026.

Closes #1365

[ptheywood]

FLAME GPU 2 compiles with CUDA 13.2 and Visual Studio 2026 in CI.

This hasn't built the test suite however, so there may be new warnings in there. We should test this locally on a windows install at some point, but this is promising.

This PR needs editing still, to use Vs 2026 but in the windows-2025 image rather than the preview, however CMake should error if we request that currently (as we explicitly list the Generator to use) so we can't do that until the new image is in use (if we want CI to pass).

I'll try and remember to do that on/after the 4th may.

---

CMake configure log from CI showing

The CUDA compiler identification is NVIDIA 13.2.51 with host compiler MSVC 19.50.35728.0

Where 19.50 is VS 2026 (in one of the three versioning schemes MS use per visual studio release...)

Run cmake . -B "build" -G "Visual Studio 18 2026" -A x64 -Werror=dev -DCMAKE_WARN_DEPRECATED="OFF" -DFLAMEGPU_WARNINGS_AS_ERRORS="ON" -DFLAMEGPU_SEATBELTS="ON" -DCMAKE_CUDA_ARCHITECTURES="75" -DFLAMEGPU_BUILD_TESTS="OFF" -DFLAMEGPU_BUILD_PYTHON="ON" -DPython3_ROOT_DIR="$(dirname $(which python))" -DPython3_EXECUTABLE="$(which python)" -DFLAMEGPU_VISUALISATION="ON" -DFLAMEGPU_ENABLE_NVTX="ON"
-- Looking for a CXX compiler
-- Looking for a CXX compiler - C:/Program Files/Microsoft Visual Studio/18/Enterprise/VC/Tools/MSVC/14.50.35717/bin/Hostx64/x64/cl.exe
-- The CXX compiler identification is MSVC 19.50.35728.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files/Microsoft Visual Studio/18/Enterprise/VC/Tools/MSVC/14.50.35717/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for a CUDA compiler
-- Looking for a CUDA compiler - C:/Program Files/NVIDIA GPU Computing Toolkit/CUDA/v13.2/bin/nvcc.exe
-- The CUDA compiler identification is NVIDIA 13.2.51 with host compiler MSVC 19.50.35728.0
-- Detecting CUDA compiler ABI info
-- Detecting CUDA compiler ABI info - done
-- Check for working CUDA compiler: C:/Program Files/NVIDIA GPU Computing Toolkit/CUDA/v13.2/bin/nvcc.exe - skipped
-- Detecting CUDA compile features
-- Detecting CUDA compile features - done
--  cpplint: NOT FOUND!
 Lint projects will not be generated.
 Please install cpplint as described on https://pypi.python.org/pypi/cpplint.
 In most cases command 'pip install cpplint' should be sufficient.
-- Found Git: C:/Program Files/Git/mingw64/bin/git.exe (found version "2.53.0.windows.2")
-- The C compiler identification is MSVC 19.50.35728.0
...

[ptheywood]

The windows-2025 image update appears to have been dalyed until June, with the origianl early may date being when the image was marked as GA

The "windows-latest" and “windows-2025” labels in GitHub Actions will be migrated to use Visual Studio 2026 by default. Customers needing Visual Studio 2022 must migrate to the windows-2022 image.

...

This change will be rolled out over a week beginning June 8, 2026 and will complete by June 15, 2026.

actions/runner-images#14017

It being a gradual roll out is going to be fun (with some jobs failing and some succeeding)...

It looks like the explicit vs2026 image label might stick around, but it might not?

We can probably just wait another month and see how it goes.