Extract resolve_nested_model helper to reduce cast() duplication

Consolidates the repeated pattern of resolving a FieldInfo's default
to a Pydantic BaseModel instance (via default or default_factory) into
a single helper. Also tightens update_description_with_new_default
parameter types from Any to object.

src/rendercv/schema/variant_pydantic_model_generator.py

@@ -29,6 +29,31 @@ def sanitize_defaults(value: Any) -> Any:
     return value
 
 
+def resolve_nested_model(field_info: FieldInfo) -> pydantic.BaseModel | None:
+    """Resolve a FieldInfo's default to a Pydantic model instance.
+
+    Why:
+        Multiple functions need to inspect whether a field's default is a nested
+        Pydantic model. The default can come from either a direct value or a
+        factory callable. This helper encapsulates the resolution and isinstance
+        check, eliminating repeated cast() calls across the module.
+
+    Args:
+        field_info: Pydantic field info to inspect.
+
+    Returns:
+        Model instance if the default is a BaseModel, otherwise None.
+    """
+    if field_info.default_factory is not None:
+        factory = cast(Callable[[], Any], field_info.default_factory)
+        obj = factory()
+        if isinstance(obj, pydantic.BaseModel):
+            return obj
+    elif isinstance(field_info.default, pydantic.BaseModel):
+        return field_info.default
+    return None
+
+
 def create_variant_pydantic_model[T: pydantic.BaseModel](
     *,
     variant_name: str,
@@ -155,15 +180,7 @@ def validate_defaults_against_base(
                 continue
 
             base_field_info = base_fields[field_name]
-            nested_obj: pydantic.BaseModel | None = None
-
-            if base_field_info.default_factory is not None:
-                factory = cast(Callable[[], Any], base_field_info.default_factory)
-                obj = factory()
-                if isinstance(obj, pydantic.BaseModel):
-                    nested_obj = obj
-            elif isinstance(base_field_info.default, pydantic.BaseModel):
-                nested_obj = base_field_info.default
+            nested_obj = resolve_nested_model(base_field_info)
 
             if nested_obj is not None:
                 nested_fields = type(nested_obj).model_fields
@@ -195,8 +212,8 @@ def generate_model_name(variant_name: str, class_name_suffix: str) -> str:
 
 def update_description_with_new_default(
     original_description: str | None,
-    old_default: Any,
-    new_default: Any,
+    old_default: object,
+    new_default: object,
 ) -> str | None:
     """Update field description to reflect new default value.
 
@@ -331,14 +348,9 @@ def create_nested_model_variant_model(
 
         if isinstance(new_value, dict):
             # Check if this field is a nested Pydantic model
-            nested_obj = None
-            if base_field_info.default_factory is not None:
-                factory = cast(Callable[[], Any], base_field_info.default_factory)
-                nested_obj = factory()
-            elif isinstance(base_field_info.default, pydantic.BaseModel):
-                nested_obj = base_field_info.default
+            nested_obj = resolve_nested_model(base_field_info)
 
-            if nested_obj is not None and isinstance(nested_obj, pydantic.BaseModel):
+            if nested_obj is not None:
                 # Recursively create nested field spec
                 field_specs[field_name] = create_nested_field_spec(
                     new_value, base_field_info
@@ -381,17 +393,7 @@ def create_nested_field_spec(
     Returns:
         Tuple of variant class annotation and Field with default_factory.
     """
-    # Get the base nested object - could be from default or default_factory
-    base_nested_obj: pydantic.BaseModel | None = None
-
-    if base_field_info.default_factory is not None:
-        # Create an instance using the factory
-        # Cast to proper callable type to satisfy type checker
-        factory = cast(Callable[[], Any], base_field_info.default_factory)
-        base_nested_obj = cast(pydantic.BaseModel, factory())
-    elif isinstance(base_field_info.default, pydantic.BaseModel):
-        # The default is already a Pydantic model instance
-        base_nested_obj = base_field_info.default
+    base_nested_obj = resolve_nested_model(base_field_info)
 
     if base_nested_obj is not None:
         # Create a variant class with updated field specs and descriptions