Make mass fraction cutoff a function argument

[jhp-lanl]

The mass fraction cutoff for the PTE solver in the get_sg_eos_* interface should be an argument that can be passed by the calling function.

The cutoff is currently a magic number in the init_functor() for the various function calls:

singularity-eos/singularity-eos/eos/get_sg_eos_functors.hpp

Line 75 in 909b83f

if (frac_mass_v(i, m) > 1.e-12) {