Improve the handling of modules and events

Take into account the proper number of modules: increment by one
pathsAndConsumes.allModules().size(), because it does not include the
"source" module.

Add asserts to check that all ranges are properly closed.

Optionally, delay starting the profiler until after the first event on
each stream has completed. This requires running 'nvprof' with the
'--profile-from-start off' option.