feat: raise TypeError if Corgy instantiated directly

corgy/_corgy.py

@@ -584,6 +584,9 @@ def add_args_to_parser(
             parser.add_argument(*var_flags, type=var_add_type, **_kwargs)
 
     def __init__(self, **args):
+        if self.__class__ is Corgy:
+            raise TypeError("`Corgy` is an abstract class and cannot be instantiated")
+
         grp_args_map: Dict[str, Any] = defaultdict(dict)
 
         for arg_name, arg_val in args.items():

tests/test_corgy.py

@@ -201,6 +201,10 @@ class D(Corgy):
         d = D(x=1, c=c)
         self.assertDictEqual(d.as_dict(), {"x": 1, "c": c})
 
+    def test_corgy_cls_raises_if_initialized_directly(self):
+        with self.assertRaises(TypeError):
+            Corgy()
+
     def test_corgy_cls_usable_without_annotations(self):
         class C(Corgy):
             ...