MUSTANG - add mass balance on lines or polygons
Transpose in CROCO the MARS feature in PHYS/TRA/submassbalance.F90 which permit to compute mass balance during the simulation on area (closed domain) or passing though lines (open domain).
Careful for MPI (need to use MPI_REDUCE)
See : https://mars3d.ifremer.fr/docs/doc.module.substance2.html for a description of the wanted feature