### What problem does this PR solve?
This PR adds fields to the `Chunk` class to store retrieval results like
similarity scores, term similarity, vector similarity, positions, and
document type. This allows the chunk object to hold all the information
needed when returning search results from the vector database.
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
- The API documentation lacks detailed error code explanations. Added
error code tables to `python_api_reference.md` and
`http_api_reference.md` to clarify possible error codes and their
meanings.
- Error handling in the codebase is inconsistent. Standardized error
handling logic in `sdk/python/ragflow_sdk/modules/chunk.py`.
- Improved API comments by adding standardized docstrings to enhance
code readability and maintainability.
### Type of change
- [x] Documentation Update
- [x] Refactoring
