[voice_assistant] Use zero-copy buffer access for audio data (#12656)

esphome/components/api/api_pb2.cpp

@@ -2527,20 +2527,22 @@ bool VoiceAssistantAudio::decode_varint(uint32_t field_id, ProtoVarInt value) {
 }
 bool VoiceAssistantAudio::decode_length(uint32_t field_id, ProtoLengthDelimited value) {
   switch (field_id) {
-    case 1:
-      this->data = value.as_string();
+    case 1: {
+      this->data = value.data();
+      this->data_len = value.size();
       break;
+    }
     default:
       return false;
   }
   return true;
 }
 void VoiceAssistantAudio::encode(ProtoWriteBuffer buffer) const {
-  buffer.encode_bytes(1, this->data_ptr_, this->data_len_);
+  buffer.encode_bytes(1, this->data, this->data_len);
   buffer.encode_bool(2, this->end);
 }
 void VoiceAssistantAudio::calculate_size(ProtoSize &size) const {
-  size.add_length(1, this->data_len_);
+  size.add_length(1, this->data_len);
   size.add_bool(1, this->end);
 }
 bool VoiceAssistantTimerEventResponse::decode_varint(uint32_t field_id, ProtoVarInt value) {