- Added 32-bit session_id to ETCP_CONN struct (random per client)
- Session_id transmitted in INIT_REQUEST/RESPONSE after node_id
- Server: skip reinit if session_id matches existing connection
- Server: send INIT_RESPONSE (0x03) only when reinit actually done
- Server: send INIT_RESPONSE_NOINIT (0x05) for same session
- Client: ignore INIT_RESPONSE with wrong session_id
- Fixed tx_state initialization in etcp_conn_ready for noinit case
- All 26 tests passing