instrument python code in gridpacks to provide timing profiles for event generation

[valassi]

I have done some work on instrumenting python code in gridpacks to provide timing profiles for event generation.

This is meant to better understand the CMS times reported by @choij1589 in #943

I am essentially done with the basics, tested this on ggtt.mad, will now test on cms DY processes too

Will add this to an existing PR (it goes hand in hand with providing multi-backend gridpacks #945)