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/base/location.cc

@@ -0,0 +1,54 @@
+// Copyright (c) 2012 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "platform/base/location.h"
+
+#include <sstream>
+
+#include "platform/base/compiler_specific.h"
+
+namespace openscreen {
+
+Location::Location() = default;
+Location::Location(const Location&) = default;
+Location::Location(Location&&) noexcept = default;
+
+Location::Location(const void* program_counter)
+    : program_counter_(program_counter) {}
+
+Location& Location::operator=(const Location& other) = default;
+Location& Location::operator=(Location&& other) = default;
+
+std::string Location::ToString() const {
+  if (program_counter_ == nullptr) {
+    return "pc:nullptr";
+  }
+
+  std::ostringstream oss;
+  oss << "pc:" << program_counter_;
+  return oss.str();
+}
+
+#if defined(__GNUC__)
+#define RETURN_ADDRESS() \
+  __builtin_extract_return_addr(__builtin_return_address(0))
+#else
+#define RETURN_ADDRESS() nullptr
+#endif
+
+// static
+OSP_NOINLINE Location Location::CreateFromHere() {
+  return Location(RETURN_ADDRESS());
+}
+
+// static
+OSP_NOINLINE const void* GetProgramCounter() {
+  return RETURN_ADDRESS();
+}
+
+std::ostream& operator<<(std::ostream& out, const Location& location) {
+  return out << location.ToString();
+}
+
+}  // namespace openscreen