Refactor library generation

examples/modular/force_reduction.cpp

examples/modular/force_reduction.py

examples/modular/sd_sample_1_CPU_GPU.cpp

examples/modular/sd_sample_2_CPU_GPU.cpp

examples/modular/sd_sample_3_CPU.cpp

examples/modular/sd_sample_3_GPU.cu

examples/modular/spring_dashpot.py

examples/whole-program-generation/spring_dashpot.py

src/pairs/code_gen/accessor.py

src/pairs/code_gen/cgen.py

src/pairs/code_gen/interface.py

src/pairs/ir/block.py

src/pairs/ir/module.py

src/pairs/mapping/funcs.py

src/pairs/sim/comm.py

src/pairs/sim/domain.py

src/pairs/sim/simulation.py