Refine observed usage

app/src/main/java/com/hippo/ehviewer/Settings.kt

@@ -111,7 +111,7 @@ object Settings : DefaultPreferences() {
     var proxyIp by stringOrNullPref("proxy_ip", null)
 
     var dohUrl by stringPref("doh_url", "")
-    var language by stringPref("app_language", "system").apply { changesFlow().observe { updateWhenLocaleChanges() } }
+    var language by stringPref("app_language", "system").observed { updateWhenLocaleChanges() }
     var lastDawnDay by longPref("last_dawn_day", 0)
 
     init {

app/src/main/java/com/hippo/ehviewer/SettingsCollector.kt

@@ -5,12 +5,11 @@ import androidx.core.os.LocaleListCompat
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.SupervisorJob
-import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.launch
+import splitties.preferences.PrefDelegate
 
 val collectScope = CoroutineScope(Dispatchers.Main + SupervisorJob())
-
-fun Flow<Unit>.observe(func: (Unit) -> Unit) = collectScope.launch { collect(func) }
+fun <T, R : PrefDelegate<T>> R.observed(func: (Unit) -> Unit) = apply { collectScope.launch { changesFlow().collect(func) } }
 
 fun updateWhenLocaleChanges() {
     val newValue = Settings.language