Modernize Particles

[ax3l]

Hi,

Let us modernize the ParticleContainer in FHDeX to use PureSoA particles and a PolymorphicArenaAllocator. This will improve FHDeX performance/runtime, simplify type complexity and potentially also reduce your compile time.

There are a registered Python types for FHDeX particles in pyAMReX and we would in the mid-term drop support for the legacy layout (w/ AoS) and the explicit allocators (all but polymorphic) to reduce compile- & link-time and increase runtime compatibility between different AMReX codes.

Please see the Particle Roadmap in AMReX/pyAMReX and let me and/or @atmyers know if you have any questions or need any help.

[ax3l]

cc @ajnonaka @WeiqunZhang @atmyers is this a small modernization to FHDeX that you could let claude/cursor/codex do on the side? Would help us to optimize compile-time in pyAMReX...

[atmyers]

It's a bit heavier than that because we need to make neighbor particles and lists in AMReX work with pure SoA first. But I will make a pass at that so we can get moving on this.