feat(audio): implement voice chat with Opus codec and streaming audio source

Add AudioStreamSource for continuous PCM playback. Refactor voice send/receive to encode with Opus and stream to a dedicated source instead of per-frame sources. Enable voice transmission over network.

include/Cubed/audio/audio_engine.hpp

@@ -3,6 +3,7 @@
 #include "Cubed/audio/audio_fade.hpp"
 #include "Cubed/audio/audio_recording.hpp"
 #include "Cubed/audio/audio_source.hpp"
+#include "Cubed/audio/audio_stream_source.hpp"
 #include "Cubed/audio/sound_manager.hpp"
 #include "Cubed/audio/source_pool.hpp"
 #include "Cubed/config.hpp"
@@ -70,6 +71,8 @@ private:
     bool m_underwater = false;
     float m_music_volume = 1.0f;
     float m_sfx_volume = 1.0f;
+
+    std::unique_ptr<AudioStreamSource> m_voice_source;
     std::unique_ptr<AudioFilter> m_low_pass_filter;
     std::unique_ptr<AudioEffect> m_underwater_effect;
     std::unique_ptr<AudioEffectSlot> m_underwater_slot;

include/Cubed/audio/audio_stream_source.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <al.h>
+#include <cstdint>
+#include <span>
+#include <vector>
+namespace Cubed {
+class AudioStreamSource {
+public:
+    static constexpr int NUM_BUFFERS = 4;
+    AudioStreamSource();
+    AudioStreamSource(const AudioStreamSource&) = delete;
+    AudioStreamSource(AudioStreamSource&&) = delete;
+    AudioStreamSource& operator=(const AudioStreamSource&) = delete;
+    AudioStreamSource& operator=(AudioStreamSource&&) = delete;
+    ~AudioStreamSource();
+
+    void push_pcm(std::span<const int16_t> pcm, ALsizei sample_rate);
+
+    void stop();
+    bool is_playing() const;
+
+private:
+    ALuint m_source = 0;
+    std::array<ALuint, NUM_BUFFERS> m_buffers{};
+    std::vector<ALuint> m_free_buffers;
+    bool m_playing = false;
+
+    void unqueue_processed();
+};
+} // namespace Cubed