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.h

@@ -0,0 +1,65 @@
+// 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.
+
+#ifndef PLATFORM_BASE_LOCATION_H_
+#define PLATFORM_BASE_LOCATION_H_
+
+#include <stddef.h>
+
+#include <cassert>
+#include <functional>
+#include <string>
+
+namespace openscreen {
+
+// NOTE: lifted from Chromium's base Location implementation, forked to work
+// with our base library.
+
+// Instances of the location class include basic information about a position
+// in program source, for example the place where an object was constructed.
+class Location {
+ public:
+  Location();
+  Location(const Location&);
+  Location(Location&&) noexcept;
+
+  // Initializes the program counter
+  explicit Location(const void* program_counter);
+
+  Location& operator=(const Location& other);
+  Location& operator=(Location&& other);
+
+  // Comparator for hash map insertion. The program counter should uniquely
+  // identify a location.
+  bool operator==(const Location& other) const {
+    return program_counter_ == other.program_counter_;
+  }
+
+  // The address of the code generating this Location object. Should always be
+  // valid except for default initialized Location objects, which will be
+  // nullptr.
+  const void* program_counter() const { return program_counter_; }
+
+  // Converts to the most user-readable form possible. This will return
+  // "pc:<hex address>".
+  std::string ToString() const;
+
+  static Location CreateFromHere();
+
+ private:
+#if defined(__clang__)
+  [[clang::annotate("raw_ptr_exclusion")]]
+#endif
+  const void* program_counter_ = nullptr;
+};
+
+std::ostream& operator<<(std::ostream& out, const Location& location);
+
+const void* GetProgramCounter();
+
+#define CURRENT_LOCATION ::openscreen::Location::CreateFromHere()
+
+}  // namespace openscreen
+
+#endif  // PLATFORM_BASE_LOCATION_H_