Address linter remarks

AKModel/utils.py

-import json
 from pathlib import Path
 
 import referencing.retrieval
 from jsonschema import Draft202012Validator
 from jsonschema.protocols import Validator
-from referencing import Registry, Resource
+from referencing import Registry
 
 from AKPlanning import settings
 
 
 def _construct_schema_path(uri: str | Path) -> Path:
+    """Construct a schema URI.
+
+    This function also checks for unallowed directory traversals
+    out of the 'schema' subfolder.
+    """
     schema_base_path = Path(settings.BASE_DIR).resolve()
     uri_path = (schema_base_path / uri).resolve()
     if not uri_path.is_relative_to(schema_base_path / "schemas"):
@@ -18,8 +22,8 @@ def _construct_schema_path(uri: str | Path) -> Path:
 
 
 @referencing.retrieval.to_cached_resource()
-def retrieve_schema(uri: str) -> str:
-    # avoid dictionary traversals
+def retrieve_schema_from_disk(uri: str) -> str:
+    """Retrieve schemas from disk by URI."""
     uri_path = _construct_schema_path(uri)
     with uri_path.open("r") as ff:
         return ff.read()
@@ -31,7 +35,7 @@ def construct_schema_validator(schema: str | dict) -> Validator:
     In particular, all schemas from the 'schemas' directory
     are loaded into the registry.
     """
-    registry = Registry(retrieve=retrieve_schema)
+    registry = Registry(retrieve=retrieve_schema_from_disk)
 
     if isinstance(schema, str):
         schema_uri = str(Path("schemas") / schema)