defer pydantic import so its an optional dep

pangeo_forge_runner/meta_yaml/schema.py

@@ -1,10 +1,6 @@
+from dataclasses import dataclass
 from typing import List, Union
 
-try:
-    from pydantic.dataclasses import dataclass
-except (ImportError, ModuleNotFoundError):
-    from dataclasses import dataclass
-
 
 @dataclass
 class RecipeObject:
@@ -44,18 +40,29 @@ class Bakery:
 
 
 @dataclass
-class MetaYaml:
+class MetaYamlMinimal:
+    # TODO: this should always be a list
+    # recipes: List[Union[RecipeObject, RecipeDictObject]]
+    recipes: Union[List[RecipeObject], RecipeDictObject]
+
+
+@dataclass
+class MetaYamlExtended(MetaYamlMinimal):
     title: str
     description: str
     pangeo_forge_version: str
     pangeo_notebook_version: str
-    recipes: Union[List[RecipeObject], RecipeDictObject]
     provenance: Provenance
     maintainers: List[Maintainer]
     bakery: Bakery
 
 
 def get_schema():
     from pydantic import TypeAdapter
+    from pydantic.dataclasses import dataclass as pydantic_dataclass
+
+    @pydantic_dataclass
+    class MetaYamlExtendedModel(MetaYamlExtended):
+        pass
 
-    return TypeAdapter(MetaYaml).json_schema()
+    return TypeAdapter(MetaYamlExtendedModel).json_schema()