Add instrumentation

runtime/pairs.hpp

runtime/thermo.hpp

runtime/timers.hpp

runtime/timing.hpp

src/pairs/code_gen/cgen.py

src/pairs/ir/module.py

src/pairs/sim/instrumentation.py

src/pairs/sim/simulation.py

src/pairs/sim/timestep.py

src/pairs/transformations/__init__.py

src/pairs/transformations/instrumentation.py