Kokkos 5.0 Support

[lsawade]

Task description

Kokkos 5.0 release candidate branch is available and ready for testing. The launch is set for 2 weeks from now (mid-nov 2025). We should eventually update the Kokkos version and upgrade to CPP 20.

• Update the CMakeList.txt
  • set(CMAKE_CXX_STANDARD 20)
• Update cmake/kokkos.cmake
  • set(KOKKOS_VERSION "5.0.00") this is not really possible yet since release is not out
• Do benchmarking
• grep and update the CPP20 TODO's

Acceptance criteria

• There is at least no slow down and tests pass.