Implement Cast Streaming mirroring, DLNA casting, daemon+GUI, and breadd integration

Builds out the full v1 scope: a vendored+patched openscreen subset for
low-latency Cast Streaming (Mirroring receiver 0F5096E8) alongside the
existing Cast V2/HLS and new DLNA/AVTransport casting paths, breadcastd's
Idle/Casting state machine with a private IPC socket, the breadcast GTK4
popup as a thin IPC client, and bread.cast.*/bread.command.cast.* breadd
integration (device discovery, start/stop, mirroring lifecycle events).
Also adds bakery/systemd/Forgejo CI packaging.

Validated end-to-end against a real Chromecast/Google TV: negotiated
Cast Streaming session, live pipeline playback, and daemon+GUI click-to-cast/
stop through the actual popup.

breadcast-caststream-sys/vendor/openscreen/cast/streaming/impl/ntp_time.cc

@@ -0,0 +1,54 @@
+// Copyright 2019 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "cast/streaming/impl/ntp_time.h"
+
+#include "util/osp_logging.h"
+
+namespace openscreen::cast {
+
+namespace {
+
+// The number of seconds between 1 January 1900 and 1 January 1970.
+constexpr NtpSeconds kTimeBetweenNtpEpochAndUnixEpoch(2208988800);
+
+}  // namespace
+
+NtpTimeConverter::NtpTimeConverter(Clock::time_point now,
+                                   std::chrono::seconds since_unix_epoch)
+    : start_time_(now),
+      since_ntp_epoch_(
+          std::chrono::duration_cast<NtpSeconds>(since_unix_epoch) +
+          kTimeBetweenNtpEpochAndUnixEpoch) {}
+
+NtpTimeConverter::~NtpTimeConverter() = default;
+
+NtpTimestamp NtpTimeConverter::ToNtpTimestamp(
+    Clock::time_point time_point) const {
+  const Clock::duration time_since_start = time_point - start_time_;
+  const auto whole_seconds =
+      std::chrono::duration_cast<NtpSeconds>(time_since_start);
+  const auto remainder =
+      std::chrono::duration_cast<NtpFraction>(time_since_start - whole_seconds);
+  return AssembleNtpTimestamp(since_ntp_epoch_ + whole_seconds, remainder);
+}
+
+Clock::time_point NtpTimeConverter::ToLocalTime(NtpTimestamp timestamp) const {
+  auto ntp_seconds = NtpSecondsPart(timestamp);
+  // Year 2036 wrap-around check: If the NTP timestamp appears to be a
+  // point-in-time before 1970, assume the 2036 wrap-around has occurred, and
+  // adjust to compensate.
+  if (ntp_seconds <= kTimeBetweenNtpEpochAndUnixEpoch) {
+    constexpr NtpSeconds kNtpSecondsPerEra{INT64_C(1) << 32};
+    ntp_seconds += kNtpSecondsPerEra;
+  }
+
+  const auto whole_seconds = ntp_seconds - since_ntp_epoch_;
+  const auto seconds_since_start =
+      Clock::to_duration(whole_seconds) + start_time_;
+  const auto remainder = Clock::to_duration(NtpFractionPart(timestamp));
+  return seconds_since_start + remainder;
+}
+
+}  // namespace openscreen::cast