Start standardizing package syntax

custom/abinit.scm

custom/atat.scm

custom/atomsk.scm

custom/cosma.scm

custom/costa.scm

custom/cp2k.scm

custom/dbcsr.scm

custom/dftb+.scm

custom/dla-future.scm

custom/elpa-openmpi-2023.scm

custom/freefem.scm

custom/gmsh.scm

custom/granoo.scm

custom/kim-api.scm

custom/lammps.scm

custom/libgrpp.scm

custom/libint.scm

custom/libxc-cp2k.scm

custom/libxc.scm

custom/libxsmm.scm