fix: handle charm status only from CollectStatus event callback

[dariofaccin]

Description

This PR aims to fix #173. Status setting is removed from the try-except block during __init__ and it now relies only on the CollectStatus event callback.
Unit tests requiring charm reinstatiation, as updated by #147, are updated evaluating the unit status.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have bumped the version of the library