Fix particle leapfrog example initialization data

[brryan]

PR Summary

The particle_leapfrog example was generating a compiler error in #910. I was able to reproduce this error with NVHPC 24.7.0/nvcc 12.5 on a Darwin volta-x86 node. Turns out we can't capture a Kokkos::Array of Kokkos::Arrays as a reference inside device code. I changed this to a copy and the code compiles for me (up to an ICE in poisson_package.cpp I am unsure about)

@fglines-nv This should fix the build error you encountered.

PR Checklist

• Code passes cpplint
• New features are documented.
• Adds a test for any bugs fixed. Adds tests for new features.
• Code is formatted
• Changes are summarized in CHANGELOG.md
• Change is breaking (API, behavior, ...)
  • Change is additionally added to CHANGELOG.md in the breaking section
  • PR is marked as breaking
  • Short summary API changes at the top of the PR (plus optionally with an automated update/fix script)
• CI has been triggered on Darwin for performance regression tests.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[fglines-nv]

I just made this same change locally. This error doesn't appear with Cuda 12.2 but does appear with Cuda 12.5. Something must have changed between then