[Experimental] Add halo cells for ghost/exchange optimization

examples/modular/sphere_box_global.cpp

runtime/domain/ParticleDataHandling.hpp

runtime/domain/block_forest.cpp

runtime/domain/regular_6d_stencil.cpp

runtime/timers.hpp

runtime/utility/dem_sc_grid.cpp

src/pairs/__init__.py

src/pairs/code_gen/interface.py

src/pairs/mapping/funcs.py

src/pairs/sim/cell_lists.py

src/pairs/sim/comm.py

src/pairs/sim/domain_partitioning.py

src/pairs/sim/simulation.py