Add a demo on pseudoheating

https://doi.org/10.1063/1.4789608
https://doi.org/10.1063/1.4863833

The idea is that particle motions guided by waves may generate pseudoheating of the distribution function if the spatial resolution is low. This is an interesting result and not difficult to reproduce.

An even more interesting investigation is that whether the conclusion will change in a self-consistent PIC simulation?

Read the two linked papers first to define the pseudoheating result and its required spatial resolution. Then inspect the repository's existing demos and particle-tracing entry points; done would mean a reproducible demo of the reported effect, while the self-consistent PIC question remains an open investigation.

Written by the indexing model from the issue text.