Some ValidityTests redundancies

[sophiafarrell]

Thanks to Luke K. on LZ, we have a couple smaller enhancements to add to our new floating point equality function. Shouldn't change any results but will make the code prettier/more logical.

• The following "else" is redundant:

if (a == b) { // shortcut, handles infinities
    return true;
  } else {

• We might want to check if https://en.cppreference.com/w/cpp/types/numeric_limits/epsilon is useful for this check. I will look into this once we get other more urgent dev done!

[sophiafarrell]

Redundancy 1 taken care of in:
b28c0cd

[sophiafarrell]

(The standard epsilon may be useful, but for now the freedom of a scaling factor to this smallest-floating difference may be less physical than the case of people being able to set epsilon to mimic some energy-separation at which point values are indistinguishable. Thus I am opting to leave as-is, for now.)