PartSysBase and SimpleSOL+particles tweaks

[oparry-ukaea]

Description

Move handling of particle output frequency into particle system base class.

Type of change

• [x] Refactoring/cleanup ~- [ ] Bug fix (non-breaking change)~ ~- [ ] New feature (non-breaking change which adds functionality)~ ~- [ ] API change (breaks downstream workflows and requires major semver bump)~ ~- [ ] Requires documentation updates~

Testing

No new tests. Passes existing unit and integration tests.

Test Configuration:

OS: Ubuntu 22.04 Compiler: GCC 11.3.0 / OneAPI v2022.1.0 SYCL implementation: Hipsycl v0.9.2 / DPC++ v2022.1.0 MPI details: MPICH v4.0.2 Hardware: CPU (Intel Alder Lake)

Checklist:

• [x] New and existing unit tests pass locally with my changes
• [x] I have used understandable variable names
• [x] I have run clang-format against my *.hpp and *.cpp changes
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings ~- [ ] I have added tests that prove my fix is effective or that my feature works~ ~- [ ] Any new dependencies are automatically built for users via cmake~ ~- [ ] I have run cmake-format against my changes to CMakeLists.txt~ ~- [ ] I have run black against changes to *.py~ ~- [ ] I have made corresponding changes to the documentation~

[oparry-ukaea]

N.B. I've only changed the parameter name in the SimpleSOL config file for now, since that's the only solver using PartSysBase at the moment. I'll update the HW/LAPD solvers and their test/example configs on feature/3DHW.

[oparry-ukaea]

Last commit just adds some explanation of how 'num_particles_total' is used in SimpleSOL.

[will-saunders-ukaea]

Unit+Integration tests passed with hipsycl.