fix: update examples in user guide to use f.to_timestamp for date extraction

Author: kosiew

docs/source/user-guide/common-operations/functions.rst

@@ -82,10 +82,11 @@ Extracting parts of a date using :py:func:`~datafusion.functions.date_part` (ali
 
 .. ipython:: python
 
-    df.select(
-        f.date_part(literal("month"), col('"event_time"')).alias("month"),
-        f.extract(literal("day"), col('"event_time"')).alias("day")
-    )
+     df.select(
+        f.date_part(literal("month"), f.to_timestamp(col('"Total"'))).alias("month"),
+        f.extract(literal("day"), f.to_timestamp(col('"Total"'))).alias("day")
+     )
+  
 String
 ------