Create a GPRT based particle-sim tool

[Waqar-ukaea]

A nice milestone for the GPRT integration will be to have an XDG tool/miniapp which performs an MC particle simulation using GPRT as the driver for particle steps forward. The idea is to start from the existing particle sim tool.

This will be pretty helpful for getting a feel for how GPRT could be used within a fully featured monte-carlo code in the future and should help inform the design of the public GPRTRayTracer API.

[Waqar-ukaea]

What we want with this will probably be a standalone tool. At first built off of the original particle simulation tool but with the ability to handle batches of particles together. Which should give us an opportunity to better end to end test and array based ray query API within XDG.

This should give us a more direct comparison against Embree in terms of performance. But it will still be bottlenecked by host to device transfers (and vice versa).

Following that, a full event based algorithm which runs entirely on the GPU to avoid expensive host-to-device device-to-host copies would be a nice proof of concept for what a monte Carlo particle transport code performing ray tracing queries against CAD entirely on GPU could look like.