refactor: periodicPlaybackTimer 계산시 initialDelay와 repeating에 있는 같은 값을 period 변수로 선언

SodaLive/Sources/Live/Room/LiveRoomViewModel.swift

@@ -1810,8 +1810,9 @@ final class LiveRoomViewModel: NSObject, ObservableObject {
     
     private func startPeriodicPlaybackValidation() {
         let queue = DispatchQueue.global(qos: .background)
+        let period = DispatchTimeInterval.seconds(1800)
         periodicPlaybackTimer = DispatchSource.makeTimerSource(queue: queue)
-        periodicPlaybackTimer?.schedule(deadline: .now() + 1800, repeating: 1800)
+        periodicPlaybackTimer?.schedule(deadline: .now() + period, repeating: period)
         periodicPlaybackTimer?.setEventHandler { [weak self] in
             self?.trackEventLiveContinuousListen30()
         }