Various robustness additions to the Davis EOS

[jhp-lanl]

PR Summary

Three primary additions to the Davis Reactants and Products EOS to make them more robust:

1. Added the robust::ratio function when dividing by density
2. Added early returns for non-positive densities. Since the products EOS should exhibit ideal gas behavior at zero density, it makes sense to return zeros for the reference values.
3. Maxed the density with zero in the reactants EOS. With the robust ratio this basically just returns a low density limit. I don't think there's an overflow issue, but I could be wrong.
4. Added the correct minimum energy as a function of density

PR Checklist

• [ ] Adds a test for any bugs fixed. Adds tests for new features.
• [x] Format your changes by using the make format command after configuring with cmake.
• N/A Document any new features, update documentation for changes made.
• [x] Make sure the copyright notice on any files you modified is up to date.
• [x] After creating a pull request, note it in the CHANGELOG.md file.
• [ ] LANL employees: make sure tests pass both on the github CI and on the Darwin CI

If preparing for a new release, in addition please check the following:

• [ ] Update the version in cmake.
• [ ] Move the changes in the CHANGELOG.md file under a new header for the new release, and reset the categories.

[jhp-lanl]

@chadmeyer please review these changes and see if you agree with my approach

[jhp-lanl]

@chadmeyer I think I addressed all your comments. I'll give things another scan and make sure I didn't miss anything else silly, but I think this is good now.

[jhp-lanl]

FYI - I added a few more robustness additions. Mainly I added an error to the DensityEnergyFromPressureTemperature() functions if the resultant density is negative (adding a max here probably will just cause the function to not converge and produce a less informative error).

I also added a robust::ratio to where we divide by Ts. It is possible for this to underflow which might be zero.