test: Add verification of deletion of local files

Verify local files used in end to end test are deleted upon completion

Test COG-488

cognee/tests/test_pgvector.py

@@ -90,6 +90,8 @@ async def main():
     assert len(history) == 6, "Search history is not correct."
 
     await cognee.prune.prune_data()
+    assert not os.path.isdir(data_directory_path), "Local files are not deleted"
+
     await cognee.prune.prune_system(metadata=True)
     tables_in_database = await vector_engine.get_table_names()
     assert len(tables_in_database) == 0, "The database is not empty"