Add some linear tests in the CI and gather lzd initialisation routines into sysprop.f90

Add linear/Locreg to bring tests for INPUT_IG_FULL cases and linear/geopt for linear restart from memory.

Also reshuffled all routines in sysprop.f90 to keep only routines in relation to system_initialisation() and move children routines scattered here and there in sysprop.f90.

Still a draft at the moment to see if I can add the coverage of sysprop.f90 in the CI (note that linear/Locreg, linear/geopt, linear/rotatesmall and linear/spin are a minimal set of tests to get a maximum coverage of sysprop.f90 at the moment).