Change Page.State to sealed interface (#1988)

(cherry picked from commit f1e2efcb37e2c623b769e979fa1c7e9e5ad7117d)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/data/download/Downloader.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderViewModel.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/ArchivePageLoader.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/EpubPageLoader.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/HttpPageLoader.kt

source-api/src/commonMain/kotlin/eu/kanade/tachiyomi/source/model/Page.kt

@@ -20,7 +20,7 @@ open class Page(
         get() = index + 1
 
     @Transient
-    private val _statusFlow = MutableStateFlow(State.QUEUE)
+    private val _statusFlow = MutableStateFlow<State>(State.Queue)
 
     @Transient
     val statusFlow = _statusFlow.asStateFlow()
@@ -49,11 +49,11 @@ open class Page(
         }
     }
 
-    enum class State {
-        QUEUE,
-        LOAD_PAGE,
-        DOWNLOAD_IMAGE,
-        READY,
-        ERROR,
+    sealed interface State {
+        data object Queue : State
+        data object LoadPage : State
+        data object DownloadImage : State
+        data object Ready : State
+        data object Error : State
     }
 }