Apply suggestions from code review

Co-authored-by: Christoph Zwerschke <c.zwerschke@dkfz-heidelberg.de>

src/metldata/builtin_transformations/delete_properties/model_transform.py

@@ -64,5 +64,5 @@ def delete_properties(
         )
 
     model_dict = model.model_dump()
-    model_dict.update({"classes": {**model.classes, **updated_class_defs}})
+    model_dict["classes"].update(updated_class_defs)
     return SchemaPack.model_validate(model_dict)

src/metldata/builtin_transformations/infer_relations/data_transform.py

@@ -44,8 +44,6 @@
           as defined in the inferred relation
 """
 
-from collections.abc import Set
-
 from schemapack.spec.custom_types import ResourceId
 from schemapack.spec.datapack import DataPack, Resource
 
@@ -96,15 +94,12 @@ def resolve_active_path_element(
     if not source_resource:
         raise EvitableTransformationError()
 
-    target_resource_ids = source_resource.relations.get(path_element.property, set())
+    target_resource_ids = source_resource.relations.get(path_element.property)
     if target_resource_ids is None:
         target_resource_ids = set()
-
-    return (
-        set(target_resource_ids)
-        if isinstance(target_resource_ids, Set)
-        else set([target_resource_ids])
-    )
+    elif isinstance(target_resource_ids, str):
+        target_resource_ids = {target_resource_ids}
+    return target_resource_ids
 
 
 def resolve_passive_path_element(