fix: default to PARQUET format in Store.for_download()

Avoid sending null format value to the backend, which doesn't accept it.

Author: mpetazzoni

wherobots/db/store.py

@@ -59,4 +59,8 @@ def for_download(cls, format: StorageFormat | None = None) -> "Store":
         Returns:
             A Store configured for single-file download with presigned URL.
         """
-        return cls(format=format, single=True, generate_presigned_url=True)
+        return cls(
+            format=format or StorageFormat.PARQUET,
+            single=True,
+            generate_presigned_url=True,
+        )