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/string_parse.h

@@ -0,0 +1,32 @@
+// Copyright 2024 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_STRING_PARSE_H_
+#define UTIL_STRING_PARSE_H_
+
+#include <charconv>
+#include <optional>
+#include <string_view>
+#include <system_error>
+
+#include "platform/base/type_util.h"
+
+namespace openscreen::string_parse {
+
+// Parses `number` into the numeric type `result` and returns true if
+// successful.  `number` must be an ASCII representation of an integer or
+// floating point value, and `result` must be compatible with the resulting
+// value.  If `number` cannot be parsed, then returns false.
+template <typename T, typename = internal::EnableIfArithmetic<T>>
+bool ParseAsciiNumber(std::string_view number, T& result) {
+  if (number.empty())
+    return false;
+  auto [unused_ptr, error_code] =
+      std::from_chars(number.data(), &number.back() + 1, result);
+  return error_code == std::errc();
+}
+
+}  // namespace openscreen::string_parse
+
+#endif  // UTIL_STRING_PARSE_H_