docs: Add deprecated mentions in visitor/inspection/hybrid extensions

Author: pawamoy

src/griffe/extensions/base.py

@@ -42,7 +42,7 @@ class When(enum.Enum):
 
 
 class VisitorExtension:
-    """The node visitor extension base class, to inherit from."""
+    """Deprecated in favor of `Extension`. The node visitor extension base class, to inherit from."""
 
     when: When = When.after_all
 
@@ -74,7 +74,7 @@ def visit(self, node: ast.AST) -> None:
 
 
 class InspectorExtension:
-    """The object inspector extension base class, to inherit from."""
+    """Deprecated in favor of `Extension`. The object inspector extension base class, to inherit from."""
 
     when: When = When.after_all
 

src/griffe/extensions/hybrid.py

@@ -1,4 +1,4 @@
-"""This extension provides an hybrid behavior while loading data."""
+"""Deprecated. This extension provides an hybrid behavior while loading data."""
 
 from __future__ import annotations