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/util/chrono_helpers.h

@@ -0,0 +1,50 @@
+// Copyright 2020 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UTIL_CHRONO_HELPERS_H_
+#define UTIL_CHRONO_HELPERS_H_
+
+#include <chrono>
+
+// This file is a collection of helpful utilities and using statement for
+// working with std::chrono. In practice we previously defined these frequently,
+// this header allows for a single set of convenience statements.
+namespace openscreen {
+
+using hours = std::chrono::hours;
+using microseconds = std::chrono::microseconds;
+using milliseconds = std::chrono::milliseconds;
+using nanoseconds = std::chrono::nanoseconds;
+using seconds = std::chrono::seconds;
+
+// Casting statements. Note that duration_cast is not a type, it's a function,
+// so its behavior is different than the using statements above.
+template <typename D>
+static constexpr hours to_hours(D d) {
+  return std::chrono::duration_cast<hours>(d);
+}
+
+template <typename D>
+static constexpr microseconds to_microseconds(D d) {
+  return std::chrono::duration_cast<microseconds>(d);
+}
+
+template <typename D>
+static constexpr milliseconds to_milliseconds(D d) {
+  return std::chrono::duration_cast<milliseconds>(d);
+}
+
+template <typename D>
+static constexpr nanoseconds to_nanoseconds(D d) {
+  return std::chrono::duration_cast<nanoseconds>(d);
+}
+
+template <typename D>
+static constexpr seconds to_seconds(D d) {
+  return std::chrono::duration_cast<seconds>(d);
+}
+
+}  // namespace openscreen
+
+#endif  // UTIL_CHRONO_HELPERS_H_