Separate the tracing of the passive and thermodynamic variables

[maxpkatz]

We have to carry around NQ variables in the construction of the final interface states, for Ip/Im (and similarly, NQSRC variables for Ip_src/Im_src). By splitting the thermodynamic and passive variables into separate arrays, there's two potential optimizations. First, we only require one wave (the middle wave) for the passive variables, so the second-to-last dimension can be size 1, not size 3. Second, we could configure the PPM reconstruction and tracing to be done one passive variable at a time, so that the passive Ip/Im could be size 1 in the last dimension, not size npassive. This optimization is necessary for being able to scale the PPM algorithm for large networks.

[zingale]

The strategy here is to break q into 3 groups:

• q_core: NQC comps, NQCSRC source comps
• q_passive: NQP comps, NQPSRC source comps (which may be 0 if we are not considering passive sources)
• q_rad: NQR comps (there are no sources for this).

Eventually, we will rename q_core -> q

[zingale]

For the 4th order, we would need a q_bar version of each.

[zingale]

important: as part of this, we need to take the velocities out of qpass_map

[zingale]

there is a better way to save memory without the complexity of separating the primitive state. This is to do the parabolic reconstruction and intergration "on demand" as done now on the actual_ppm branch.