stcp: ed25519 pubkey exchange in handshake, fix instance destroy segfault, fix chat_tcp_test

- u_async.c: process immediate_queue BEFORE epoll_wait in uasync_poll
- stcp_link.c: defensive NULL etcp_conn/etcp_link in stcp_link_close
- utun_instance.c: move stcp_server_list_destroy_all to Phase J (before ETCP),
  add deferred drain in both Phase J and L
- stcp.h/c: STCP_HS_ENC_CLIENT 6→38, STCP_HS_ENC_SERVER 7→39,
  exchange ed25519_pubkey in both handshake directions
- etcp_connections.c: copy peer_ed25519 from STCP to ETCP_CONN in
  etcp_link_enter_ready_tcp; guard link->etcp in tcp_link_close_cb
- chat_sync.c: fix lk->conn NULL dereference for TCP links
- test_stcp.c: update stcp_server_create/stcp_client_connect callsites
- tools/chat_tcp_test: change transport udp→tcp

tools/chatgui/zxing-cpp/core/src/ByteArray.h

@@ -0,0 +1,42 @@
+/*
+* Copyright 2016 Nu-book Inc.
+* Copyright 2022 Axel Waggershauser
+*/
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include "Range.h"
+
+#include <cstdint>
+#include <string_view>
+#include <vector>
+
+namespace ZXing {
+
+/**
+	ByteArray is an extension of std::vector<uint8_t>.
+*/
+class ByteArray : public std::vector<uint8_t>
+{
+public:
+	ByteArray() = default;
+	ByteArray(std::initializer_list<uint8_t> list) : std::vector<uint8_t>(list) {}
+	explicit ByteArray(int len) : std::vector<uint8_t>(len, 0) {}
+	explicit ByteArray(std::string_view str) : std::vector<uint8_t>(str.begin(), str.end()) {}
+
+	void append(ByteView other) { insert(end(), other.begin(), other.end()); }
+	void append(std::string_view other) { insert(end(), other.begin(), other.end()); }
+
+	std::string_view asString(size_t pos = 0, size_t len = std::string_view::npos) const
+	{
+		return std::string_view(reinterpret_cast<const char*>(data()), size()).substr(pos, len);
+	}
+
+	ByteView asView(size_t pos = 0, size_t len = size_t(-1)) const
+	{
+		return ByteView(*this).subview(pos, len);
+	}
+};
+
+} // ZXing