[newchem-cpp] Cleanup initialization of kcol_rate_tables

[mabruzzo]

This PR must be reviewed after #411 is merged

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Overview

At a high-level this PR:

• deletes initialize_metal_chemistry_rates.cpp
• mutates initialize_rates.cpp
• creates init_misc_species_cool_rates.cpp
• creates collisional_rate_props.cpp

In more detail, all functionality that was previously in initialize_metal_chemistry_rates.cpp has been split between init_misc_species_cool_rates.cpp and collisional_rate_props.cpp.

• We moved all logic relating to initializing 2body reaction rates (i.e. for primordial_chemistry 4 & metal chemistry) from initialize_metal_chemistry_rates.cpp into collisional_rate_props.cpp.
• We moved all other logic (that namely pertains to initializing species-specific cooling) out of initialize_metal_chemistry_rates.cpp and into init_misc_species_cool_rates.cpp. (this file probably needs more cleanup, but that's beyond the scope of this PR

Let's talk more about collisional_rate_props.cpp:

As part of this PR:

• I broke out the logic for each primordial_chemistry==4 and metal_chemistry collisional rate. These functions are analogous to the existing rate functions (k1_rate, k2_rate, ...)¹
• I created a grackle::impl::visit_rate_props function that effectively iterates through all standardized collisional reaction rate functions. This includes all of the existing primordial_chemistry= 1,2, and 3 functions as well as the new primordial_chemistry=4 and metal_chemistry=1 rates.
• I have slightly refactored the logic contained within the initialize_rates.cpp to make use of grackle::impl::visit_rate_props to actually initialize the standardized collisional reaction rate functions.

Overall, I think this leads to much cleaner code. Now that we have ~88² of the standardized collisional reaction rate functions. I have structured it in the current manner for reasons that should become apparent once #415 is finished

Footnotes

1. I left comments that explain the work that should be done before we are ready to expose all the new rate functions as part of the public API ↩

2. At the moment, I'm taking a very broad definition of "standard". In the future, one might imagine treating a handful of rates more specially again. Examples of such rates include: k13 (due to the existence of k13dd), k56 (since we use it to infer a deuterium rate), as well as the 3 body rates. ↩

[mabruzzo]

@brittonsmith -- this should be ready to go

[brittonsmith]

I have done a much deeper literature search than I thought I would (more than 10 papers) and have yet to find a reference to this experiment or that temperature range. Dalgarno & Black (1976) equation 2.28 had several references that I chased down, but at that point I can no longer see the rate appear in the same functional form.

This all begins with Omukai (2000), which is the primary source for nearly all the gas-phase reaction rates (as I think this model was explicitly derived from that). Nonetheless, I agree that I see no evidence that we are applying any form of truncation of this rate.

[brittonsmith]

UPDATE: a googling of the temperature range itself turned up this:
https://www.aanda.org/articles/aa/full_html/2017/11/aa30388-17/aa30388-17.html
I don't have time to dig deeper into the context here, but it looks like this comes from a UMIST database (which is ironically the first place I went after Omukai 2000.

Again, it doesn't look like we're actually doing anything with this information. I'm going to leave this here as I really REALLY have to get home now. Feel free to update the comment (or not) and I'll merge this in the morning.