style: apply pyink formatting and add return type annotation

Author: enjoykumawat

src/google/adk/artifacts/file_artifact_service.py

@@ -76,9 +76,7 @@ def _validate_path_segment(value: str, name: str) -> None:
   if not value:
     raise InputValidationError(f"{name} must not be empty.")
   if any(sep in value for sep in ("/", "\\", "..")):
-    raise InputValidationError(
-        f"{name} contains invalid characters: {value!r}"
-    )
+    raise InputValidationError(f"{name} contains invalid characters: {value!r}")
 
 
 _USER_NAMESPACE_PREFIX = "user:"

tests/unittests/artifacts/test_artifact_service.py

@@ -783,7 +783,7 @@ async def test_file_save_artifact_rejects_absolute_path_within_scope(tmp_path):
 )
 async def test_file_save_artifact_rejects_path_traversal_in_ids(
     tmp_path, user_id, session_id
-):
+) -> None:
   """FileArtifactService rejects user_id/session_id with path traversal."""
   artifact_service = FileArtifactService(root_dir=tmp_path / "artifacts")
   part = types.Part(text="content")