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.h

@@ -0,0 +1,73 @@
+// 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.
+
+#ifndef CAST_STREAMING_IMPL_NTP_TIME_H_
+#define CAST_STREAMING_IMPL_NTP_TIME_H_
+
+#include <stdint.h>
+
+#include "platform/api/time.h"
+
+namespace openscreen::cast {
+
+// NTP timestamps are 64-bit timestamps that consist of two 32-bit parts: 1) The
+// number of seconds since 1 January 1900; and 2) The fraction of the second,
+// where 0 maps to 0x00000000 and each unit increment represents another 2^-32
+// seconds.
+//
+// Note that it is part of the design of NTP for the seconds part to roll around
+// on 7 February 2036.
+using NtpTimestamp = uint64_t;
+
+// NTP fixed-point time math: Declare two std::chrono::duration types with the
+// bit-width necessary to reliably perform all conversions to/from NTP format.
+using NtpSeconds = std::chrono::duration<int64_t, std::chrono::seconds::period>;
+using NtpFraction =
+    std::chrono::duration<int64_t, std::ratio<1, INT64_C(0x100000000)>>;
+
+constexpr NtpSeconds NtpSecondsPart(NtpTimestamp timestamp) {
+  return NtpSeconds(timestamp >> 32);
+}
+
+constexpr NtpFraction NtpFractionPart(NtpTimestamp timestamp) {
+  return NtpFraction(timestamp & 0xffffffff);
+}
+
+constexpr NtpTimestamp AssembleNtpTimestamp(NtpSeconds seconds,
+                                            NtpFraction fraction) {
+  return (static_cast<uint64_t>(seconds.count()) << 32) |
+         static_cast<uint32_t>(fraction.count());
+}
+
+// Converts between Clock::time_points and NtpTimestamps. The class is
+// instantiated with the current Clock time and the current wall clock time, and
+// these are used to determine a fixed origin reference point for all
+// conversions. Thus, to avoid introducing unintended timing-related behaviors,
+// only one NtpTimeConverter instance should be used for converting all the NTP
+// timestamps in the same streaming session.
+class NtpTimeConverter {
+ public:
+  NtpTimeConverter(
+      Clock::time_point now,
+      std::chrono::seconds since_unix_epoch = GetWallTimeSinceUnixEpoch());
+  ~NtpTimeConverter();
+
+  NtpTimestamp ToNtpTimestamp(Clock::time_point time_point) const;
+  Clock::time_point ToLocalTime(NtpTimestamp timestamp) const;
+
+ private:
+  // The time point on the platform clock's timeline that corresponds to
+  // approximately the same time point on the NTP timeline. Note that it is
+  // acceptable for the granularity of the NTP seconds value to be whole seconds
+  // here: Both a Cast Streaming Sender and Receiver will assume their clocks
+  // can be off (with respect to each other) by even a large amount; and all
+  // that matters is that time ticks forward at a reasonable pace from some
+  // initial point.
+  const Clock::time_point start_time_;
+  const NtpSeconds since_ntp_epoch_;
+};
+
+}  // namespace openscreen::cast
+
+#endif  // CAST_STREAMING_IMPL_NTP_TIME_H_