### What problem does this PR solve?
当前graphrag的LOOP_PROMPT，会导致模型输出Y之后，继续补充了实体和关系，比较浪费时间。参照[graph
rag](https://github.com/microsoft/graphrag/blob/main/graphrag/prompts/index/extract_graph.py)最新的代码，修改了LOOP_PROMPT，经过验证，修改后可以稳定的输出Y停止。
Currently, GraphRAG’s LOOP_PROMPT causes the model to keep appending
entities and relationships even after outputting “Y,” which wastes time.
Referring to the latest code in
[graphRAG](https://github.com/microsoft/graphrag/blob/main/graphrag/prompts/index/extract_graph.py),
I modified the LOOP_PROMPT, and after verification the updated prompt
reliably outputs “Y” and stops.
### Type of change
- [ ] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [x] Performance Improvement
- [ ] Other (please describe):
Co-authored-by: liuzhenghua-jk <liuzhenghua-jk@360shuke.com>
### What problem does this PR solve?
Removed set_entity and set_relation to avoid accessing doc engine during
graph computation.
Introduced GraphChange to avoid writing unchanged chunks.
### Type of change
- [x] Performance Improvement
