Refactor clock usage and mod generator

kernel/sched/fair.c

kernel/sched/idle_task.c

kernel/sched/pb.c

kernel/sched/sched.h

pb_utils/add_to_img.sh

pb_utils/execute_tests.pl

pb_utils/mod_gen/mods/Makefile

pb_utils/mod_gen/mods/plan_same_v.c

pb_utils/mod_gen/mods/random_v.c

pb_utils/mod_gen/plan_to_module.pl

pb_utils/mod_gen/plans/random_v.csv