Title basically...
cfg connections now need to have `prepare` called on them (context manager will do this for you), but unless `dedicated_connection` is set to `True` they now basically assume you are going to leave the scrapli connection alone (i.e. scrapli-cfg will not open/close the underlying scrapli conn w/out that `dedicated_connection` arg).
`on_open` --> `on_prepare` and the default callable have been removed -- too much magic, users can/should provide an `on_prepare` to handle whatever they need for their environment.
Closer to a stable public release (2021.07.30 of course)