rename create_timestamp_flt to create_timestamp_float (#2473)

### What problem does this PR solve?


### Type of change

- [x] Performance Improvement

sdk/python/ragflow/modules/chunk.py

         self.content = ""
         self.important_keywords = []
         self.create_time = ""
-        self.create_timestamp_flt = 0.0
+        self.create_timestamp_float = 0.0
         self.knowledgebase_id = None
         self.document_name = ""
         self.document_id = ""
                          "content_with_weight": self.content,
                          "important_kwd": self.important_keywords,
                          "create_time": self.create_time,
-                         "create_timestamp_flt": self.create_timestamp_flt,
+                         "create_timestamp_flt": self.create_timestamp_float,
                          "doc_id": self.document_id,
                          "status": self.status,
                          })