Simplify the application run/stop cycle

The lib should provide a way to handle the application bootstrapping and finishing (in several ways: ok, error, etc).

The code is already in Charmcraft, we need to move it in here.

Start by comparing the existing application bootstrapping and finishing implementation in Charmcraft with the current lib. Identify how successful and error outcomes are handled, then determine what must move into this project. Done means the library provides the requested run/stop cycle and handles the listed completion paths consistently.

Written by the indexing model from the issue text.