Name of EZFIO file. It is obtained from the QPACKAGE_INPUT environment
variable if it is set, or as the 1st argument of the command line.
`getunitandopen <http://github.com/LCPQ/quantum_package/tree/master/src/Ezfio_files/get_unit_and_open.irp.f#L/integer function getUnitAndOpen(f,mode)/;"