refactor: Unify Actor context manager with init & exit methods

[vdusek]

Description

To align the behavior between the two possible approaches of using an Actor - as a context manager or by explicitly calling init/exit/fail - the following changes were implemented:

• The Actor's arguments (exit_code, status_message, event_listeners_timeout, cleanup_timeout) were added to the Actor.__init__ as well.
• exit_code and status_message are now public properties with setters, allowing them to be updated within a context manager block in response to error conditions.
• The previous approach of calling __aenter__ from init and __aexit__ from exit was reversed, ensuring fewer inconsistencies for future changes (since __aenter__ and __aexit__ have a fixed number of arguments).

Other changes:

• Related docstrings were updated.
• The ordering of methods in the Actor was adjusted (see ruff issue #2425).
• The interface of init, exit, and fail remains unchanged.

Issues

• Closes: Unify Actor's context manager with manual init/exit methods #598

Testing

• The current test set cover the changes.