Fix: Increase sync wait time for 1-connection under network latency

- Dynamically scale wait time based on latency and connection count
- 1 connection gets additional latency-proportional wait time
- Added extra sync calls after server shutdown
- Prevents verification failures due to slow disk writes under WAN conditions

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

benchmark_network.sh

@@ -232,14 +232,22 @@ run_fastsync() {
     local output
     output=$(timeout 300 "$CLIENT_BIN" -h "$HOST" -p "$port" -s "$SRC_DIR" -n "$nconn" 2>&1) || true
     
-    # With network latency, wait longer for all data to be written
-    # 1 conn needs more time under latency
-    local wait_time=8
-    [ "$nconn" -eq 1 ] && wait_time=10
+    # With network latency, wait longer for all data to be written and synced to disk
+    # Scale wait time based on latency: base wait + (latency factor * connection count factor)
+    # 1 connection needs significantly more time under high latency
+    local base_wait=$(( LATENCY_MS * 2 / 10 ))
+    local conn_factor=$(( 16 / nconn ))
+    local wait_time=$(( base_wait + conn_factor + 5 ))
+    [ "$wait_time" -lt 10 ] && wait_time=10
+    [ "$nconn" -eq 1 ] && wait_time=$(( wait_time + LATENCY_MS / 5 + 5 ))
+    
+    info "Waiting ${wait_time}s for sync to complete..."
     sleep $wait_time
     kill "$spid" 2>/dev/null || true
     wait "$spid" 2>/dev/null || true
     sync
+    sleep 2
+    sync
     
     local ms=$(echo "$output" | grep -oP 'ms=\K[0-9.]+' || echo "0")
     local mbs=$(echo "$output" | grep -oP 'throughput_mbs=\K[0-9.]+' || echo "0")