refactor: STCP connections as ETCP links (is_tcp)

- Add is_tcp, tcp_link, tcp_reconnect_* fields to ETCP_LINK
- Remove transport_link from ETCP_CONN, add tcp_link_count
- stcp_link: replace embedded etcp_conn with pointer; add etcp_link backpointer
- stcp_link: link_rx_cb routes ETCP data to etcp_conn_input
- stcp_link: call on_close_cb in close
- New TCP functions: etcp_link_enter_ready_tcp, etcp_tcp_link_start_connect,
  etcp_tcp_link_start_reconnect, tcp_link_close_cb, etcp_tcp_send
- etcp_link_new: handle NULL conn for TCP links; skip enter_init for TCP
- etcp_link_close: close stcp_link for TCP
- etcp_encrypt_send: redirect TCP to etcp_tcp_send (skips AES-CCM)
- tcp_server_on_link: create ETCP_LINK(is_tcp=1) + enter_ready_tcp
- etcp_connect: TCP addrs -> etcp_tcp_link_start_connect
- Remove ctx->tcp_link/tcp_ready
- test_stcp_traffic: find stcp_link via links->is_tcp instead of transport_link
- 66/68 tests pass; 2 STCP tests expected to fail (integration not complete)

tools/chatgui/zxing-cpp/core/src/TextDecoder.cpp

@@ -1,54 +0,0 @@
-/*
-* Copyright 2016 Nu-book Inc.
-* Copyright 2022 gitlost
-* Copyright 2025 Axel Waggershauser
-*/
-// SPDX-License-Identifier: Apache-2.0
-
-#include "TextDecoder.h"
-
-#include "ZXAlgorithms.h"
-#include "libzueci/zueci.h"
-
-#include <cassert>
-#include <stdexcept>
-#include <cstdio>
-
-namespace ZXing {
-
-std::string BytesToUtf8(ByteView bytes, ECI eci)
-{
-	constexpr unsigned int replacement = 0xFFFD;
-	constexpr unsigned int flags = ZUECI_FLAG_SB_STRAIGHT_THRU | ZUECI_FLAG_SJIS_STRAIGHT_THRU;
-	int utf8_len;
-
-	if (eci == ECI::Unknown)
-		eci = ECI::Binary;
-
-	int error_number = zueci_dest_len_utf8(ToInt(eci), bytes.data(), Size(bytes), replacement, flags, &utf8_len);
-	if (error_number >= ZUECI_ERROR) {
-#ifdef PRINT_DEBUG
-		fprintf(stderr, "zueci_dest_len_utf8 error: %d\n", error_number);
-#endif
-		// throw FormatError("Invalid UTF-8 data");
-		return {};
-	}
-
-	std::string utf8(utf8_len, 0);
-
-	error_number = zueci_eci_to_utf8(ToInt(eci), bytes.data(), Size(bytes), replacement, flags,
-									 reinterpret_cast<uint8_t*>(utf8.data()), &utf8_len);
-	if (error_number >= ZUECI_ERROR) {
-#ifdef PRINT_DEBUG
-		fprintf(stderr, "zueci_eci_to_utf8 error: %d\n", error_number);
-#endif
-		// throw FormatError("Invalid UTF-8 data");
-		return {};
-	}
-
-	assert(Size(utf8) == utf8_len);
-
-	return utf8;
-}
-
-} // ZXing