Use Kotlin Duration for SECONDS_PER_HOUR in WooPosProductRestClient

Replaces manual calculation of seconds per hour with Kotlin's `Duration` API for improved readability and consistency.

Author: malinajirka

libs/fluxc-plugin/src/main/kotlin/org/wordpress/android/fluxc/network/rest/wpcom/wc/product/pos/WooPosProductRestClient.kt

@@ -17,6 +17,7 @@ import java.time.ZoneOffset
 import java.time.format.DateTimeFormatter
 import java.util.Locale
 import javax.inject.Inject
+import kotlin.time.Duration.Companion.hours
 
 class WooPosProductRestClient @Inject constructor(
     private val wooNetwork: WooNetwork,
@@ -31,7 +32,7 @@ class WooPosProductRestClient @Inject constructor(
             "regular_price,sale_price,date_modified,stock_quantity,stock_status,manage_stock," +
             "backordered,attributes,image,downloadable,name,type"
 
-        private const val SECONDS_PER_HOUR = 3600
+        private val SECONDS_PER_HOUR = 1.hours.inWholeSeconds
 
         private val API_DATE_FORMATTER = DateTimeFormatter
             .ofPattern("yyyy-MM-dd'T'HH:mm:ss", Locale.US)