[restored issue] - Rename the module hiepacs "solverstack"
The packages defined in inria/hiepacs.scm are mainly softwares hosted in the group solverstack on gitlab.inria. Hence, we should rename hiepacs solverstack. And move the packages related to compose in inria/concace.scm or create a new module compose.scm for it, so that the module name does not depend on an Inria team (which is not persistent).
Warning: this issue has been restored from backup and can have been changed. For example, all comments have been lost.