Add --duration, --csv, --quiet flags for automated testing

- --duration N: run client test for N seconds then exit
- --csv <file>: append results to CSV (creates with headers if new)
- --quiet/-q: suppress terminal output (for scripted/machine use)

CSV columns: timestamp, host, port, protocol, direction, duration_s,
  tx_avg_mbps, rx_avg_mbps, tx_bytes, rx_bytes, lost_packets, auth_type

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/csv_output.rs

@@ -0,0 +1,83 @@
+//! CSV output for machine-readable test results.
+//!
+//! Appends a row per test to the specified CSV file.
+//! Creates the file with headers if it doesn't exist.
+
+use std::fs::OpenOptions;
+use std::io::Write;
+use std::path::Path;
+use std::sync::Mutex;
+use std::time::SystemTime;
+
+static CSV_FILE: Mutex<Option<String>> = Mutex::new(None);
+static QUIET: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+
+const HEADER: &str = "timestamp,host,port,protocol,direction,duration_s,tx_avg_mbps,rx_avg_mbps,tx_bytes,rx_bytes,lost_packets,auth_type";
+
+/// Initialize CSV output. Creates file with headers if needed.
+pub fn init(path: &str) -> std::io::Result<()> {
+    let needs_header = !Path::new(path).exists() || std::fs::metadata(path)?.len() == 0;
+
+    if needs_header {
+        let mut f = OpenOptions::new().create(true).write(true).open(path)?;
+        writeln!(f, "{}", HEADER)?;
+    }
+
+    *CSV_FILE.lock().unwrap() = Some(path.to_string());
+    Ok(())
+}
+
+pub fn set_quiet(q: bool) {
+    QUIET.store(q, std::sync::atomic::Ordering::Relaxed);
+}
+
+pub fn is_quiet() -> bool {
+    QUIET.load(std::sync::atomic::Ordering::Relaxed)
+}
+
+/// Write a test result row to the CSV file.
+pub fn write_result(
+    host: &str,
+    port: u16,
+    protocol: &str,
+    direction: &str,
+    duration_secs: u64,
+    tx_bytes: u64,
+    rx_bytes: u64,
+    lost_packets: u64,
+    auth_type: &str,
+) {
+    let guard = CSV_FILE.lock().unwrap();
+    if let Some(ref path) = *guard {
+        let tx_mbps = if duration_secs > 0 {
+            tx_bytes as f64 * 8.0 / duration_secs as f64 / 1_000_000.0
+        } else {
+            0.0
+        };
+        let rx_mbps = if duration_secs > 0 {
+            rx_bytes as f64 * 8.0 / duration_secs as f64 / 1_000_000.0
+        } else {
+            0.0
+        };
+
+        let now = SystemTime::now()
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs();
+
+        let row = format!(
+            "{},{},{},{},{},{},{:.2},{:.2},{},{},{},{}",
+            now, host, port, protocol, direction, duration_secs,
+            tx_mbps, rx_mbps, tx_bytes, rx_bytes, lost_packets, auth_type,
+        );
+
+        if let Ok(mut f) = OpenOptions::new().append(true).open(path) {
+            let _ = writeln!(f, "{}", row);
+        }
+    }
+}
+
+/// Check if CSV output is enabled.
+pub fn is_enabled() -> bool {
+    CSV_FILE.lock().unwrap().is_some()
+}