Initial: ContinuousTransponder wrapper for Kogger USBL

High-level Python wrapper around the upstream cosma-tech/kogger_acousticAntenna
driver. Configures a Kogger acoustic antenna as a permanent slave transponder
in a single start() call: address filter, echo filter, optional TDMA sync slot,
permanent response window, and Python callbacks for each ping received.

No modification to the upstream driver — only composes existing public methods
in the right order. Snapshot of upstream driver included read-only under driver/
for reference.

Includes:
- transponder_continu.py (302 lines): the wrapper class + CLI
- examples/auv_slave.py (79 lines): usage example with logging
- README.md: design rationale, usage, multi-AUV TDMA, watchdog, hardware wiring
- driver/: snapshot of cosma-tech/kogger_acousticAntenna at commit 1b539f9
  ('Add index slot for multi pinger', 2025-03-11)

Built for Cosma context (USV master + N AUVs slaves) following the design
conversation in Discord #ping-pong-ping (2026-04-27). See poulpe/ping-pong-ping
on Gitea for the interactive demo of the protocol.

examples/auv_slave.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+"""
+Exemple : un AUV slave Kogger en mode transpondeur continu.
+
+Le master USV envoie des pings adressés. Cet AUV répond automatiquement, logge
+chaque ping reçu (timestamp, SNR, distance hardware), et publie en parallèle
+sur stdout. Aucun arming par ping requis.
+
+Lancement :
+    python3 auv_slave.py --port /dev/ttyUSB0 --address 2 --vehicle AUV-2
+
+Pour intégrer dans un nœud ROS2 / NATS / MQTT, remplacer `on_ping` ci-dessous
+par un publisher.
+"""
+
+import argparse
+import time
+import sys
+
+sys.path.insert(0, "..")  # rend transponder_continu.py importable depuis examples/
+from transponder_continu import ContinuousTransponder, SyncSlot
+
+
+def main():
+    p = argparse.ArgumentParser()
+    p.add_argument("--port", required=True)
+    p.add_argument("--address", type=int, required=True)
+    p.add_argument("--vehicle", default="AUV")
+    p.add_argument("--slot-total", type=int, default=0,
+                   help="Si >0 : enrôle l'AUV dans un slot TDMA partagé.")
+    p.add_argument("--slot-duration", type=float, default=2.0)
+    args = p.parse_args()
+
+    sync = None
+    if args.slot_total > 0:
+        sync = SyncSlot(
+            slot_total=args.slot_total,
+            slot_index=args.address - 1,  # convention : slot index = address - 1
+            slot_duration=args.slot_duration,
+        )
+
+    t = ContinuousTransponder(
+        port=args.port,
+        my_address=args.address,
+        vehicle_name=args.vehicle,
+        sync=sync,
+        watchdog_timeout_s=15.0,  # re-arm si silence > 15 s (USV down ?)
+    )
+
+    pings_log = []
+
+    def on_ping(msg):
+        rec = {
+            "t_local": time.time(),
+            "id": msg.get("id"),
+            "snr": msg.get("snr"),
+            "distance_m": t.state.last_distance_m,
+            "raw": msg,
+        }
+        pings_log.append(rec)
+        print(
+            f"[{rec['t_local']:.3f}] ping #{t.state.pings_received} "
+            f"id={rec['id']} snr={rec['snr']} "
+            f"d={rec['distance_m']:.2f}m" if rec['distance_m'] else "d=—"
+        )
+
+    t.on_ping_received(on_ping)
+
+    print(f"=== {args.vehicle} en transpondeur continu, address={args.address} ===")
+    t.start()
+    try:
+        t.run_forever()
+    finally:
+        t.stop()
+        print(f"\nFin de session. {len(pings_log)} pings reçus au total.")
+
+
+if __name__ == "__main__":
+    main()