Fix BeforeValidator import (#212)

Author: caroljung-cg

src/codegen/sdk/codebase/span.py

@@ -1,6 +1,7 @@
 from typing import Annotated, Any
 
-from pydantic import BaseModel, BeforeValidator, ConfigDict, WithJsonSchema
+from pydantic import BaseModel, ConfigDict, WithJsonSchema
+from pydantic.functional_validators import BeforeValidator
 from pydantic.json_schema import JsonSchemaValue
 from pydantic_core.core_schema import ValidationInfo
 from tree_sitter import Point, Range