Cholla_PM: Fixed Cross Flux Error

Now every row along the X axis has the exact same evolution and there are no cross fluxes. The issue was that originally for the \(p \nabla \cdot \mathbf{v}\) term on the advected internal energy energy the value of \(\nabla \cdot \mathbf{v}\) was computed on th same kernel were the conserved variables were updated, this means that there was a synchronization error because it was using values of the neighbors velocities to compute \(\nabla \cdot \mathbf{v}\) and at the same time those velocities were being updated.

The solution was to add the \(p \nabla \cdot \mathbf{v}\) term to the internal energy in a separate kernel before the Update_Conserved kernel.