Add beartype for runtime type checking during development

omicron/ssg/__init__.py

@@ -0,0 +1,11 @@
+import os
+
+typechecked = os.environ.get("OSSG_TYPECHECKED")
+if typechecked == "all":
+    from beartype.claw import beartype_all
+
+    beartype_all()
+elif typechecked:
+    from beartype.claw import beartype_this_package
+
+    beartype_this_package()

omicron/ssg/content.py

@@ -7,6 +7,8 @@ from typing import TYPE_CHECKING, Any, cast
 
 if TYPE_CHECKING:
     from omicron.ssg.site import Site
+else:
+    Site = "omicron.ssg.site.Site"
 
 import yaml
 from markupsafe import Markup