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/simple_fraction.cc

@@ -0,0 +1,52 @@
+// 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.
+
+#include "util/simple_fraction.h"
+
+#include <cmath>
+#include <limits>
+#include <string>
+#include <vector>
+
+#include "util/osp_logging.h"
+#include "util/string_parse.h"
+#include "util/string_util.h"
+#include "util/stringprintf.h"
+
+namespace openscreen {
+
+// static
+ErrorOr<SimpleFraction> SimpleFraction::FromString(std::string_view value) {
+  if (value.size() > 0 && value.at(0) == '/') {
+    return Error::Code::kParameterInvalid;
+  }
+
+  std::vector<std::string_view> fields = string_util::Split(value, '/');
+  if (fields.size() != 1 && fields.size() != 2) {
+    return Error::Code::kParameterInvalid;
+  }
+
+  int numerator;
+  int denominator = 1;
+  if (!string_parse::ParseAsciiNumber(fields[0], numerator)) {
+    return Error::Code::kParameterInvalid;
+  }
+
+  if (fields.size() == 2) {
+    if (!string_parse::ParseAsciiNumber(fields[1], denominator)) {
+      return Error::Code::kParameterInvalid;
+    }
+  }
+
+  return SimpleFraction(numerator, denominator);
+}
+
+std::string SimpleFraction::ToString() const {
+  if (denominator_ == 1) {
+    return std::to_string(numerator_);
+  }
+  return StringFormat("{}/{}", numerator_, denominator_);
+}
+
+}  // namespace openscreen