graph: Remove debug prefix from Timestamp value parse errors

The TIMESTAMP_SCALAR branch accidentally formatted parse failures as "xxx{value}". Report the invalid input string directly, consistent with other ValueParseError paths.

Author: cuiweixie

graph/src/data/store/mod.rs

@@ -371,7 +371,7 @@ impl Value {
                         Value::Timestamp(scalar::Timestamp::parse_timestamp(s).map_err(|_| {
                             QueryExecutionError::ValueParseError(
                                 "Timestamp".to_string(),
-                                format!("xxx{}", s),
+                                format!("{}", s),
                             )
                         })?)
                     }