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

api/db/db_models.py

@@ -50,7 +50,6 @@ class TextFieldType(Enum):
     MYSQL = "LONGTEXT"
     OCEANBASE = "LONGTEXT"
     POSTGRES = "TEXT"
-    POSTGRES = "TEXT"
 
 
 class LongTextField(TextField):