Fix typo: documnet_keyword -> document_keyword in Chunk class (#13531)

### What problem does this PR solve?
The Chunk class had a typo in the attribute name 'documnet_keyword',
which caused the document_name field to remain empty when retrieving
chunks via the SDK. This fix corrects the spelling to
'document_keyword'.

Changes:
- Line 36: Changed self.documnet_keyword to self.document_keyword
- Line 52: Updated backward compatibility code to use
self.document_keyword


### Type of change

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

sdk/python/ragflow_sdk/modules/chunk.py

@@ -33,7 +33,7 @@ class Chunk(Base):
         self.create_timestamp = 0.0
         self.dataset_id = None
         self.document_name = ""
-        self.documnet_keyword = ""
+        self.document_keyword = ""
         self.document_id = ""
         self.available = True
         # Additional fields for retrieval results
@@ -49,7 +49,7 @@ class Chunk(Base):
 
         #for backward compatibility
         if not self.document_name:
-            self.document_name = self.documnet_keyword
+            self.document_name = self.document_keyword
 
 
     def update(self, update_message: dict):