[GL#88] Link mass and energy balances #164

Imported automatically from GitLab.

Original GitLab issue: https://gitlab.pam-retd.fr/thermosysproandco/ThermoSysPro/-/work_items/88
Original GitLab IID: 88
Original author: SIMONINI Giorgio (@giorgio.simonini) (GitHub: @Sonyoyo)

Original creation date: 2024-06-05T18:58:19.439Z
Original update date: 2025-09-05T11:12:48.359Z

In the mass balance equation, the BQ term (right size) is equal to der(M) (left side) which is then decomposed as a function of P and h and the derivative of density to these states: ddph and ddhp (see also #156 (formerly GL#80)).
In the energy balance equation, the left side is der(uM) which is then decomposed, once again, as a function of Pand h which use the same properties ddhp and ddph.
I am wondering whether it would increase numerical efficiency to better link the two equations instead of resolve two times the same terms:
$der(uM)=Mder(u)+uder(M)=Mder(u)+uBQ$.