Fix: Make separator default consistent across application

- Changed default separator in sort_for_self_referencing() from ',' to ';'
- This matches the application-wide default used in preflight.py
- Eliminates inconsistency between function default and call site default
- Updated tests to explicitly pass ',' separator where needed for test data
- Addresses review comment about inconsistent defaults for the same parameter

This change improves consistency and maintainability by ensuring the same
default separator is used throughout the application.

Author: bosd

src/odoo_data_flow/lib/sort.py

@@ -14,7 +14,7 @@ def sort_for_self_referencing(
     id_column: str,
     parent_column: str,
     encoding: str = "utf-8",
-    separator: str = ",",
+    separator: str = ";",
 ) -> Optional[Union[str, bool]]:
     """Sorts a CSV file for self-referencing hierarchies.