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/platform/impl/logging_test.h

@@ -0,0 +1,24 @@
+// 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 PLATFORM_IMPL_LOGGING_TEST_H_
+#define PLATFORM_IMPL_LOGGING_TEST_H_
+
+#include <string>
+#include <vector>
+
+// These functions should only be called from logging unittests.
+
+namespace openscreen {
+
+// Append logging output to `messages`.  Each log entry will be written as a new
+// element including a newline.  Pass nullptr to stop appending output.  Calling
+// this does not affect the behavior of SetLogFifoOrDie().  Normally this should
+// only be called for tests as it creates an append-only buffer of log messages
+// in memory.
+void SetLogBufferForTest(std::vector<std::string>* messages);
+
+}  // namespace openscreen
+
+#endif  // PLATFORM_IMPL_LOGGING_TEST_H_