docs: improve StateChart docstrings and complete 3.1.0 release notes (#609)

Author: fgmacedo

docs/releases/3.1.0.md

@@ -170,4 +170,14 @@ machine instance concurrently. This is now documented in the
   The docstring also now includes a `deprecated` directive for Sphinx autodoc.
   [#604](https://github.com/fgmacedo/python-statemachine/issues/604).
 
+- `Configuration.add()`/`discard()` now write through the model setter, ensuring state
+  changes are persisted correctly on domain models (e.g., Django models with custom setters).
+  Previously the configuration was updated in-place without notifying the model layer.
+  [#596](https://github.com/fgmacedo/python-statemachine/pull/596).
+
+- `States.from_enum()` now works correctly inside compound and parallel states. Previously
+  the states were silently not collected when used as a nested state declaration.
+  [#607](https://github.com/fgmacedo/python-statemachine/pull/607),
+  fixes [#606](https://github.com/fgmacedo/python-statemachine/issues/606).
+
 ## Misc in 3.1.0

statemachine/statemachine.py

@@ -55,9 +55,13 @@ class StateChart(Generic[TModel], metaclass=StateMachineMetaclass):
         start_value: An optional start state value if there's no current state assigned
             on the :ref:`domain models`. Default: ``None``.
 
-        listeners: An optional list of objects that provies attributes to be used as callbacks.
+        listeners: An optional list of objects that provides attributes to be used as callbacks.
             See :ref:`listeners` for more details.
 
+        **kwargs: Additional keyword arguments available for dependency injection into
+            callbacks. These are passed to class listener ``setup()`` methods and to the
+            initial activation callbacks (e.g. ``on_enter_<state>``).
+
     """
 
     TransitionNotAllowed = TransitionNotAllowed
@@ -145,9 +149,13 @@ def __init__(
         **kwargs: Any,
     ):
         self.model: TModel = model if model is not None else Model()  # type: ignore[assignment]
-        self.history_values: Dict[
-            str, List[State]
-        ] = {}  # Mapping of compound states to last active state(s).
+        """The external model object that holds domain state, or an internal
+        :class:`Model` instance when none is provided.  See :ref:`domain models`."""
+
+        self.history_values: Dict[str, List[State]] = {}
+        """Mapping from compound state IDs to the list of states that were active
+        the last time that compound state was exited. Used by history pseudo-states
+        to restore previous configurations."""
         self.state_field = state_field
         self.start_configuration_values = (
             [start_value] if start_value is not None else list(self.start_configuration_values)
@@ -416,6 +424,7 @@ def current_state(self, value):
 
     @property
     def events(self) -> "List[Event]":
+        """List of all :ref:`Event` instances declared on this state machine."""
         return [getattr(self, event) for event in self.__class__._events]
 
     @property