feat: 컨슈머 레코드 처리 기능 구현

- 메트릭 측정(ref: ce20f85c)을 위한 로직
- 레코드 자체를 처리하는 비즈니스 로직은 없음.

src/main/java/com/sangdol/consumer/infrastructure/kafka/consumer/RecordProcessor.java

@@ -0,0 +1,58 @@
+package com.sangdol.consumer.infrastructure.kafka.consumer;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.kafka.clients.consumer.ConsumerRecord;
+import org.apache.kafka.clients.consumer.ConsumerRecords;
+
+import com.sangdol.consumer.domain.TestRecord;
+import com.sangdol.consumer.infrastructure.kafka.producer.DLTProducer;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+@RequiredArgsConstructor
+public class RecordProcessor {
+
+	private static final int POLL_COMPLETION_THRESHOLD = 5;
+	private final DLTProducer dltProducer;
+	private final ConsumerStats consumerStats;
+	private final AtomicInteger emptyPollResultCount = new AtomicInteger(0);
+	private long initialRecordReceivedTime = 0;
+
+	public void process(ConsumerRecords<String, TestRecord> records) throws Exception {
+		initializeTime();
+
+		log.debug("[RecordProcessor] process {} records. thread: {}", records.count(),
+			Thread.currentThread().getName());
+		for (ConsumerRecord<String, TestRecord> record : records) {
+			try {
+				// 별도의 로직은 없음. 필요시 추가
+			} catch (Exception e) {
+				log.error("[ConsumerWorker] failed to consume record, sending to DLT. offset: {}",
+					record.offset(), e);
+				dltProducer.sendToDeadLetterTopic(record.key(), record.value(), e);
+			}
+		}
+	}
+
+	public void processIfEmptyRecords() {
+		if (initialRecordReceivedTime != 0) {
+			emptyPollResultCount.incrementAndGet();
+		}
+
+		if (emptyPollResultCount.get() == POLL_COMPLETION_THRESHOLD) {
+			long elapsedTime = System.currentTimeMillis() - initialRecordReceivedTime;
+			consumerStats.update(elapsedTime);
+			initialRecordReceivedTime = 0;
+			emptyPollResultCount.set(0);
+		}
+	}
+
+	private void initializeTime() {
+		if (initialRecordReceivedTime == 0) {
+			initialRecordReceivedTime = System.currentTimeMillis();
+		}
+	}
+}