fix(tunnel): Fixes the delayed display logic to correctly handle microsecond-level delays.

- Adjust the delayed formatting function to prioritize checking if the delay is 0 to avoid displaying errors.
- When the delay is less than 1 millisecond, it is displayed in microseconds to improve the precision of the expression.
feat (constants): Shorten heart rate intervals and timeouts to improve response speed.
- Adjust HeartbeatInterval from 5 seconds to 2 seconds
- Adjust HeartbeatTimeout from 15 seconds to 6 seconds
- Improve the sensitivity of heartbeat detection between the client and the server

internal/client/cli/ui/tunnel.go

@@ -158,13 +158,13 @@ func RenderRetrying(interval time.Duration) string {
 
 // formatLatency formats latency with color
 func formatLatency(d time.Duration) string {
-	ms := d.Milliseconds()
-	var style lipgloss.Style
-
-	if ms == 0 {
+	if d == 0 {
 		return mutedStyle.Render("measuring...")
 	}
 
+	ms := d.Milliseconds()
+	var style lipgloss.Style
+
 	switch {
 	case ms < 50:
 		style = lipgloss.NewStyle().Foreground(latencyFastColor)
@@ -176,6 +176,11 @@ func formatLatency(d time.Duration) string {
 		style = lipgloss.NewStyle().Foreground(latencyRedColor)
 	}
 
+	if ms == 0 {
+		us := d.Microseconds()
+		return style.Render(fmt.Sprintf("%dµs", us))
+	}
+
 	return style.Render(fmt.Sprintf("%dms", ms))
 }