fix(wc): flush stdout before printing deferred error

Ensure deferred error messages are printed after all stats output, matching GNU wc behavior. Added io::stdout().flush() to guarantee buffered output is written before showing the error.

Author: mattsu2020

src/uu/wc/src/wc.rs

@@ -973,6 +973,7 @@ fn wc(inputs: &Inputs, settings: &Settings) -> UResult<()> {
         }
         // Print deferred error after stats to match GNU wc output order
         if let Some(err) = deferred_error {
+            let _ = io::stdout().flush();
             show!(err);
         }
     }