Add feature props to accessor, fix issue with non scalar types

examples/modular/sd_sample_3_GPU.cu

examples/modular/spring_dashpot.py

src/pairs/code_gen/accessor.py

src/pairs/code_gen/cgen.py

src/pairs/ir/device.py

src/pairs/ir/features.py

src/pairs/sim/simulation.py

src/pairs/transformations/devices.py