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/hashing.h

@@ -0,0 +1,55 @@
+// 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 UTIL_HASHING_H_
+#define UTIL_HASHING_H_
+
+#include <cstdint>
+#include <utility>
+#include <vector>
+
+namespace openscreen {
+
+// This value is taken from absl::Hash implementation.
+inline constexpr uint64_t kDefaultSeed = UINT64_C(0xc3a5c85c97cb3127);
+
+// Computes the aggregate hash of the provided hashable objects.
+// Seed must initially use a large prime between 2^63 and 2^64 as a starting
+// value, or the result of a previous call to this function.
+template <typename... T>
+uint64_t ComputeAggregateHash(uint64_t original_seed, const T&... objs) {
+  auto hash_combiner = [](uint64_t current_seed,
+                          uint64_t hash_value) -> uint64_t {
+    static const uint64_t kMultiplier = UINT64_C(0x9ddfea08eb382d69);
+    uint64_t a = (hash_value ^ current_seed) * kMultiplier;
+    a ^= (a >> 47);
+    uint64_t b = (current_seed ^ a) * kMultiplier;
+    b ^= (b >> 47);
+    b *= kMultiplier;
+    return b;
+  };
+
+  uint64_t result = original_seed;
+  std::vector<uint64_t> hashes = {std::hash<T>()(objs)...};
+  for (uint64_t hash : hashes) {
+    result = hash_combiner(result, hash);
+  }
+  return result;
+}
+
+template <typename... T>
+uint64_t ComputeAggregateHash(const T&... objs) {
+  return ComputeAggregateHash(kDefaultSeed, objs...);
+}
+
+struct PairHash {
+  template <typename TFirst, typename TSecond>
+  size_t operator()(const std::pair<TFirst, TSecond>& pair) const {
+    return ComputeAggregateHash(pair.first, pair.second);
+  }
+};
+
+}  // namespace openscreen
+
+#endif  // UTIL_HASHING_H_