Cantera adapters expect T /P to be scalars and crash if they are lists

[alongd]

RMG reactors accept T / P both as floats and as lists, but the Cantera adapters send these values w/o modification to Cantera as a (T0, P0, X0) tuple. If T / P are indeed lists, T3/Cantera crash.
Need to fix the adapters to allow T / P in a reactor to be a list.

Would we like to take the average value of the list? Or iterate through it?