### What problem does this PR solve?
Refactor: speed up ragflow server, save startup memory, saved 200MiB,
and 5-9 seconds start time.
##### Before
1241292 | | \_ python3 api/ragflow_server.py
RAGFlow server is ready after 25.61845850944519s initialization.
##### After
1019968 | | \_ python3 api/ragflow_server.py
RAGFlow server is ready after 16.205134391784668s initialization.
### Type of change
- [x] Refactoring