Dedicated IdealGas interface in python

[vegardjervell]

Hey,

Specifically for the KineticGas package I've found it would be very nice if thermopack had an IdealGas class on the python side (essentially just exposing ideal.f90 I would assume?), because we need to compute some ideal gas properties in order to get transport properties at infinite dilution. Until now I've just used a minimalistic IdealGas class, but recently it's become apparent that having access to the ideal gas heat capacity polynomials from thermopack, without needing to initialise a "full" eos, would be useful.

I don't know how much work it would be to expose such a class in thermopack? @morteham @ailoa