Building off of#2835, this PR replaces the remaining instances ofstack() withstack(0), so that we avoid getting context information for the first frame of the stack, which is expensive.

I also discovered that we were callingtraceback.format_list(traceback.extract_stack()[-10:]), which does the following:

1. Extract the entire stack
2. Format the entire stack into strings
3. Throw away everything except for the last 10 formatted frames of the stack

To fix this, I've madeextract_stack() use thelimit=10 parameter.

Finally, I optimized_path_utils.py to only retrieve two frames from the stack, instead of retrieving the entire stack and then discarding everything but the second frame :)