[fix] Correct timestamp calculation in dify instrumentation (#74)

Author: Cirilla-zmh

instrumentation-loongsuite/loongsuite-instrumentation-dify/src/opentelemetry/instrumentation/dify/utils.py

@@ -5,11 +5,7 @@
 def get_timestamp_from_datetime_attr(obj, attr_name):
     attr_value = getattr(obj, attr_name, None)
     if attr_value is not None and isinstance(attr_value, datetime):
-        timestamp = (
-            attr_value.timestamp() * 1_000_000_000
-            + attr_value.microsecond * 1_000
-        )
-        return int(timestamp)
+        return int(attr_value.timestamp() * 1_000_000_000)
     return time.time_ns()