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.

driver/test/log/2026-03-20_14-37-46_AUV_usbl.csv

@@ -0,0 +1,7 @@
+2026-03-20 14:37:46.615358,SENT,"b'\xbbU\x00\x03\x04\x00\x07\x11'"
+2026-03-20 14:37:46.646959,SENT,"b'\xbbU\x00\x03 \x00#I'"
+2026-03-20 14:37:46.678407,SENT,"b'\xbbU\x00\x03!\x00$K'"
+2026-03-20 14:37:46.710030,SENT,"b'\xbbU\x00\x03e\x00h\xd3'"
+2026-03-20 14:37:46.741664,SENT,"b'\xbbU\x00\xa2h\x04\x00\x00\x00\x00\x0e\xf2'"
+2026-03-20 14:37:46.763085,SENT,"b'\xbbU\x00\x9ah\x04\xff\xff\xff\xff\x02\xb0'"
+2026-03-20 14:37:46.784460,SENT,"b'\xbbU\x00\xaah\x01\xff\x12\xe1'"