### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

Issue link:#[[Link the issue
here](https://github.com/infiniflow/ragflow/issues/226)]

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

* support snapshot download from local

* let snapshot download from local

* fix position extraction bug

* remove delimiter for naive parser