refactor: timeAgo 함수

- LocalDateTime 확장함수 처리

src/main/kotlin/kr/co/vividnext/sodalive/extensions/LocalDateTimeExtensions.kt

@@ -0,0 +1,18 @@
+package kr.co.vividnext.sodalive.extensions
+
+import java.time.Duration
+import java.time.LocalDateTime
+
+fun LocalDateTime.getTimeAgoString(): String {
+    val now = LocalDateTime.now()
+    val duration = Duration.between(this, now)
+
+    return when {
+        duration.toMinutes() < 1 -> "방금 전"
+        duration.toMinutes() < 60 -> "${duration.toMinutes()}분전"
+        duration.toHours() < 24 -> "${duration.toHours()}시간전"
+        duration.toDays() < 30 -> "${duration.toDays()}일전"
+        duration.toDays() < 365 -> "${duration.toDays() / 30}개월전"
+        else -> "${duration.toDays() / 365}년전"
+    }
+}