Fix children type to be compatible with Transition; misc. cleanup

Author: jiwon-oai

chatkit/actions.py

@@ -12,12 +12,14 @@
 DEFAULT_LOADING_BEHAVIOR: LoadingBehavior = "auto"
 
 
-direct_usage_of_action_classes_deprecated = deprecated(
-    "Direct usage of Action classes are deprecated; use WidgetTemplate to build widgets from .widget files/definitions instead."
+_direct_usage_of_action_classes_deprecated = deprecated(
+    "Direct usage of named action classes is deprecated. "
+    "Use WidgetTemplate to build widgets from .widget files instead. "
+    "Visit https://widgets.chatkit.studio/ to author widget files."
 )
 
 
-@direct_usage_of_action_classes_deprecated
+@_direct_usage_of_action_classes_deprecated
 class ActionConfig(BaseModel):
     type: str
     payload: Any = None
@@ -29,7 +31,7 @@ class ActionConfig(BaseModel):
 TPayload = TypeVar("TPayload")
 
 
-@direct_usage_of_action_classes_deprecated
+@_direct_usage_of_action_classes_deprecated
 class Action(BaseModel, Generic[TType, TPayload]):
     type: TType = Field(default=TType, frozen=True)  # pyright: ignore
     payload: TPayload = None  # pyright: ignore - default to None to allow no-payload actions