Fix: remove unused imports and f-string formatting (#12935)

### What problem does this PR solve?

- Remove unused imports (Mock, patch, MagicMock, json, os,
RAGFLOW_COLUMNS, VECTOR_FIELD_PATTERN) from multiple files
- Replace f-string formatting with regular strings for console output
messages in cli.py
- Clean up unnecessary imports that were no longer being used in the
codebase

### Type of change

- [x] Refactoring

tests/unit/test_oceanbase_peewee.py

@@ -3,7 +3,6 @@ Tests for OceanBase Peewee ORM support.
 """
 
 import pytest
-from unittest.mock import Mock, patch, MagicMock
 from api.db.db_models import (
     RetryingPooledOceanBaseDatabase,
     PooledDatabase,