### What problem does this PR solve?
Fix https://github.com/infiniflow/ragflow/issues/13388
Call get_flatted_meta_by_kbs in dify retrieval. Remove get_meta_by_kbs.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Avoid getting doc in function delete_document_metadata as the doc might
have been removed.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Fix [#13210](https://github.com/infiniflow/ragflow/issues/13210)
Remove limit in _search_metadata, use pagination in _search_metadata.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
This PR fixes missing metadata on documents synced from the Moodle
connector, especially for **Book** modules.
Background:
- Moodle Book metadata includes fields like `chapters`, which is a
`list[dict]`.
- During metadata normalization in
`DocMetadataService._split_combined_values`, list deduplication used
`dict.fromkeys(...)`.
- `dict.fromkeys(...)` fails for unhashable values (like `dict`),
causing metadata update to fail.
- Result: documents were imported, but metadata was not saved for
affected module types (notably Books).
What this PR changes:
- Replaces hash-based list deduplication with `dedupe_list(...)`, which
safely handles unhashable list items while preserving order.
- This allows Book metadata (and other complex list metadata) to be
persisted correctly.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):
Contribution during my time at RAGcon GmbH.
### What problem does this PR solve?
Fix "metadata table not exists" when updating a meta data.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
test_update_document.py failed as metadata is not included in the
response of get_list(), fix the issue.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
### What problem does this PR solve?
Put document metadata in ES/Infinity.
Index name of meta data: ragflow_doc_meta_{tenant_id}
### Type of change
- [x] Refactoring
