Fix cell lists and do not lift expressions across loop kernels

examples/lj.py

src/pairs/analysis/__init__.py

src/pairs/analysis/devices.py

src/pairs/ir/loops.py

src/pairs/sim/cell_lists.py

src/pairs/sim/simulation.py

src/pairs/transformations/__init__.py

src/pairs/transformations/devices.py

src/pairs/transformations/loops.py