Improve time sync logging visibility

Add retry loop with per-attempt logging for NTS time sync, making it
easy to diagnose slow NTS-KE handshakes in boot logs.

Author: kvinwang

dstack-util/src/system_setup.rs

@@ -708,10 +708,23 @@ pub async fn cmd_sys_setup(args: SetupArgs) -> Result<()> {
 async fn do_sys_setup(stage0: Stage0<'_>) -> Result<()> {
     if stage0.shared.app_compose.secure_time {
         info!("Waiting for the system time to be synchronized");
-        cmd! {
-            chronyc waitsync 20 0.1;
+        let mut last_err = None;
+        for i in 1..=30 {
+            match cmd! { chronyc waitsync 1 0.2; } {
+                Ok(_) => {
+                    last_err = None;
+                    break;
+                }
+                Err(e) => {
+                    info!("Time sync attempt {i}/30 failed, retrying...");
+                    last_err = Some(e);
+                    tokio::time::sleep(Duration::from_secs(1)).await;
+                }
+            }
+        }
+        if let Some(e) = last_err {
+            return Err(e).context("Failed to sync system time after 30 attempts");
         }
-        .context("Failed to sync system time")?;
     } else {
         info!("System time will be synchronized by chronyd in background");
     }