Suggestion to set Pitzer as the default activity model for aqueous solutions

[allanleal]

Hi @avdudchenko and @lbianchi-lbl,

First off, congratulations on developing this very nice high-level library using Reaktoro!

As discussed in this thread, I’d like to propose a change: setting the Pitzer model as the default activity model for aqueous solutions, particularly when the pitzer.dat thermodynamic database is the default.

This would lead to more accurate and consistent calculations for the aqueous solutions.