[newchem-cpp] `make_consistent` seems totally wrong for grain growth or destruction

[mabruzzo]

FYI, it appears that make_consistent may implement blatantly wrong behavior for the multi-grain model when modelling growth or destruction (I haven't really checked the case when growth/cooling is disabled -- but I would be surprised if its a problem).

I hope I'm wrong about this! And I'm simply misunderstanding things.

Anyway as far as I can tell, it seems like we enforce that the total density of nuclides in the gas phase is conserved and the total density of nuclides in dust is conserved.

Let me walk through a slightly more concrete example with some made up examples. Say 75% of Carbon is initially injected in the gas phase and 25% is initially injected in the various dust species (amorphous carbon, volatile organics, etc.). At the end of timestep, make_consistent adjusts species densities such that 75% of Carbon still resides in the gas phase and 25% still resides in the dust phase.

This seems blatantly incorrect if you are modelling growth or destructing. If I'm correct about what is going on, then this "smells" to me like a short-term hack to deal with a bug or instability that Gen forgot about. Hopefully it isn't masking significant flaws