fix: avoid 10s client dally delay by default

crates/pfs-tftp-sync/src/client.rs

@@ -32,7 +32,10 @@ impl Default for ClientConfig {
             timeout,
             retries: 5,
             dally_timeout: timeout,
-            dally_retries: 2,
+            // RFC 1350, Section 6: The final ACK sender *may* terminate immediately, but
+            // "dallying is encouraged". For CLI UX, default to no dallying and allow
+            // opt-in via flags.
+            dally_retries: 0,
         }
     }
 }