Revisit screening prescriptions to include electron-ion polarization effects

While working on "screening" (electron-ion polarization effects) in the EOS, A. Y. Potekhin made the following comments on the nuclear reactions screening in MESA:

the prescriptions by Chugunov et al. (2007) for screening of nuclear reactions ignore the electron-ion polarization and therefore are not very accurate. For the classical nuclei, the old prescription by Salpeter & van Horn (1969) is even better. A more accurate prescription, which takes into account the polarization and also matches the Chugunov et al.'s results for strong quantum limit, is that of our paper with Gilles Chabrier, A&A 538, A115 (2012).

This might be useful info in future work on screening, so noting it here.

Start by locating the EOS screening implementation and identifying where the Chugunov et al. (2007) nuclear-reaction prescription is applied. Read the cited Potekhin and Chabrier A&A 538, A115 (2012) paper and compare its electron-ion polarization treatment with the current behavior; done means an agreed, validated replacement prescription is implemented.