fix: handle missing pydantic-core corner case

src/cappa/class_inspect.py

@@ -186,13 +186,14 @@ def from_cls(cls, obj: type) -> ClassTypes | None:
             return cls.msgspec
 
         try:
+            from pydantic import BaseModel
             import pydantic
         except ImportError:  # pragma: no cover
             pass
         else:
             try:
                 is_base_model = isinstance(obj, type) and issubclass(
-                    obj, pydantic.BaseModel
+                    obj, BaseModel
                 )
             except TypeError:  # pragma: no cover
                 is_base_model = False