feat: 리플렉션 제거 - InflowControlManager.getGroupBucket() public 메서드 추가

groupBucketList private 필드에 리플렉션 없이 접근할 수 있도록
getGroupBucket(String groupId) public 메서드 제공.

그룹 테이블 테스트 픽스처 SQL 추가 및 InflowControlManagerTest에
getGroupBucket() 동작 검증 테스트 케이스 2개 추가.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/java/com/eactive/eai/common/inflow/InflowControlManager.java

@@ -371,6 +371,10 @@ public class InflowControlManager implements Lifecycle, Bucket {
 		return groupIds;
 	}
 
+	public CustomGroupBucket getGroupBucket(String groupId) {
+		return groupBucketList.get(groupId);
+	}
+
 	private CustomBucket makeBucketUsingInflowVO(InflowTargetVO inflowTarget) {
 		if (InflowControlManager.isInflowTarget(inflowTarget)) {
 			LocalBucketBuilder builder = Bucket4j.builder();