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/processors/no_audio_processor.h

@@ -0,0 +1,32 @@
+#ifndef DUMMY_AUDIO_PROCESSOR_H
+#define DUMMY_AUDIO_PROCESSOR_H
+
+#include <vector>
+#include <functional>
+
+#include "audio_processor.h"
+#include "audio_codec.h"
+
+class NoAudioProcessor : public AudioProcessor {
+public:
+    NoAudioProcessor() = default;
+    ~NoAudioProcessor() = default;
+
+    void Initialize(AudioCodec* codec) override;
+    void Feed(const std::vector<int16_t>& data) override;
+    void Start() override;
+    void Stop() override;
+    bool IsRunning() override;
+    void OnOutput(std::function<void(std::vector<int16_t>&& data)> callback) override;
+    void OnVadStateChange(std::function<void(bool speaking)> callback) override;
+    size_t GetFeedSize() override;
+    void EnableDeviceAec(bool enable) override;
+
+private:
+    AudioCodec* codec_ = nullptr;
+    std::function<void(std::vector<int16_t>&& data)> output_callback_;
+    std::function<void(bool speaking)> vad_state_change_callback_;
+    bool is_running_ = false;
+};
+
+#endif