refactor the two link emulator labs

common/Makefile

common/include/utils.h

common/link_emulator/.clang-format

common/link_emulator/Makefile

common/link_emulator/lib.c

common/link_emulator/lib.h

common/link_emulator/link.c

common/link_emulator/link.h

common/link_emulator/queue.c

common/link_emulator/queue.h

common/run_experiment.sh

common/utils.c

lab2/Makefile

lab2/common.h

lab2/link_emulator

lab2/link_emulator.err

lab2/link_emulator.out

lab2/link_emulator/Makefile

lab2/link_emulator/lib.c

lab2/link_emulator/lib.h