Add ESP32-C3 Opus loopback example

Software/UPSoftware/examples/OpusLoopbackEsp32C3/OpusLoopbackEsp32C3.ino

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+#include <Arduino.h>
+#include <AudioTools.h>
+#include <AudioTools/AudioCodecs/CodecOpus.h>
+
+using namespace audio_tools;
+
+constexpr int I2S_BCLK = 6;
+constexpr int I2S_LRC = 7;
+constexpr int I2S_DIN = 5;
+
+// Keep the test intentionally light so it is realistic for an ESP32-C3.
+AudioInfo audioInfo(16000, 1, 16);
+SineWaveGenerator<int16_t> sineWave(10000);
+GeneratedSoundStream<int16_t> source(sineWave);
+I2SStream i2s;
+OpusAudioEncoder opusEncoder;
+OpusAudioDecoder opusDecoder;
+EncodedAudioStream decodedAudio(&i2s, &opusDecoder);
+EncodedAudioStream encodedAudio(&decodedAudio, &opusEncoder);
+StreamCopy copier(encodedAudio, source);
+
+void setup() {
+  Serial.begin(115200);
+  AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Warning);
+
+  auto i2sConfig = i2s.defaultConfig(TX_MODE);
+  i2sConfig.copyFrom(audioInfo);
+  i2sConfig.pin_bck = I2S_BCLK;
+  i2sConfig.pin_ws = I2S_LRC;
+  i2sConfig.pin_data = I2S_DIN;
+  i2sConfig.buffer_count = 8;
+  i2sConfig.buffer_size = 256;
+  i2s.begin(i2sConfig);
+
+  auto sineConfig = sineWave.defaultConfig();
+  sineConfig.copyFrom(audioInfo);
+  sineWave.begin(sineConfig, N_B4);
+
+  auto &encoderConfig = opusEncoder.config();
+  encoderConfig.copyFrom(audioInfo);
+  encoderConfig.application = OPUS_APPLICATION_RESTRICTED_LOWDELAY;
+  encoderConfig.bitrate = 24000;
+  encoderConfig.complexity = 1;
+  encoderConfig.frame_sizes_ms_x2 = OPUS_FRAMESIZE_20_MS;
+
+  decodedAudio.begin(audioInfo);
+  encodedAudio.begin(audioInfo);
+
+  Serial.println("Opus loopback test started");
+}
+
+void loop() {
+  if (copier.copy() == 0) {
+    delay(1);
+  }
+}

Software/UPSoftware/examples/OpusLoopbackEsp32C3/README.md

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+This sketch is a minimal ESP32-C3 Opus codec smoke test.
+
+What it does:
+- Generates a sine wave locally
+- Encodes it with Opus
+- Decodes it immediately again
+- Sends the decoded PCM to I2S
+
+Why this example:
+- It tests the raw Opus codec path without Ogg or CAN framing
+- It is closer to the later Pi -> CAN -> ESP32 decoder path than MP3
+- It keeps CPU load down by using 16 kHz mono and low encoder complexity
+
+Expected hardware:
+- ESP32-C3
+- I2S DAC / amp on:
+  - BCLK = GPIO 6
+  - LRCK = GPIO 7
+  - DIN = GPIO 5
+
+Required Arduino libraries:
+- `arduino-audio-tools`
+- `arduino-libopus`
+
+If this sketch runs and outputs a stable sine tone, the basic Opus encode/decode
+chain is working on the ESP32-C3.