Refa:improve excel parser logic (#13372)

### What problem does this PR solve?

improve excel parser logic

### Type of change
- [x] Refactoring

deepdoc/parser/excel_parser.py

@@ -74,9 +74,16 @@ class RAGFlowExcelParser:
 
         return df.apply(lambda col: col.map(clean_string))
 
+    @staticmethod
+    def _fill_worksheet_from_dataframe(ws, df: pd.DataFrame):
+        for col_num, column_name in enumerate(df.columns, 1):
+            ws.cell(row=1, column=col_num, value=column_name)
+        for row_num, row in enumerate(df.values, 2):
+            for col_num, value in enumerate(row, 1):
+                ws.cell(row=row_num, column=col_num, value=value)
+
     @staticmethod
     def _dataframe_to_workbook(df):
-        # if contains multiple sheets use _dataframes_to_workbook
         if isinstance(df, dict) and len(df) > 1:
             return RAGFlowExcelParser._dataframes_to_workbook(df)
 
@@ -84,30 +91,19 @@ class RAGFlowExcelParser:
         wb = Workbook()
         ws = wb.active
         ws.title = "Data"
-
-        for col_num, column_name in enumerate(df.columns, 1):
-            ws.cell(row=1, column=col_num, value=column_name)
-
-        for row_num, row in enumerate(df.values, 2):
-            for col_num, value in enumerate(row, 1):
-                ws.cell(row=row_num, column=col_num, value=value)
-
+        RAGFlowExcelParser._fill_worksheet_from_dataframe(ws, df)
         return wb
-    
+
     @staticmethod
     def _dataframes_to_workbook(dfs: dict):
         wb = Workbook()
         default_sheet = wb.active
         wb.remove(default_sheet)
-        
+
         for sheet_name, df in dfs.items():
             df = RAGFlowExcelParser._clean_dataframe(df)
             ws = wb.create_sheet(title=sheet_name)
-            for col_num, column_name in enumerate(df.columns, 1):
-                ws.cell(row=1, column=col_num, value=column_name)
-            for row_num, row in enumerate(df.values, 2):
-                for col_num, value in enumerate(row, 1):
-                    ws.cell(row=row_num, column=col_num, value=value)
+            RAGFlowExcelParser._fill_worksheet_from_dataframe(ws, df)
         return wb
 
     @staticmethod