forestplot Fix extrapad

In forestplot/graph_utils.py, extrapad was calculated as xlim[1] * (1 + extrapad) which becomes extremely large when effects are not close to 0. These lines were refactored into a function _get_pad() which uses the range xlim[1] - xlim[0] as reference to compute the pad, which fixes the issue.

Modified some of the code to work without internet connection. Some of the code was trying to access csv's from https://github.com/LSYS/forestplot/tree/main/examples/data those csv's are available as a part of this repo. It now first checks if csvs are available in .[forestplot]/examples/data or a user provided Path else it access them through the url.