v1.8.0: Audio 代码重构与低功耗优化 (#943)

* Reconstruct Audio Code

* Remove old IoT implementation

* Add MQTT-UDP documentation

* OTA升级失败时，可以继续使用

main/audio/wake_word.h

@@ -0,0 +1,25 @@
+#ifndef WAKE_WORD_H
+#define WAKE_WORD_H
+
+#include <string>
+#include <vector>
+#include <functional>
+
+#include "audio_codec.h"
+
+class WakeWord {
+public:
+    virtual ~WakeWord() = default;
+    
+    virtual void Initialize(AudioCodec* codec) = 0;
+    virtual void Feed(const std::vector<int16_t>& data) = 0;
+    virtual void OnWakeWordDetected(std::function<void(const std::string& wake_word)> callback) = 0;
+    virtual void Start() = 0;
+    virtual void Stop() = 0;
+    virtual size_t GetFeedSize() = 0;
+    virtual void EncodeWakeWordData() = 0;
+    virtual bool GetWakeWordOpus(std::vector<uint8_t>& opus) = 0;
+    virtual const std::string& GetLastDetectedWakeWord() const = 0;
+};
+
+#endif