Move cache pruning to a WorkManager worker (#3649)

- Extend what was `NotificationWorkerFactory` to `WorkerFactory`. This
  can construct arbitrary Workers as long as they provide their own
  Factory for construction.

  The per-Worker factory contains any injected components just for that
  worker type, keeping `WorkerFactory` clean.

- Move `NotificationWorkerFactory` to the new model.

- Implement `PruneCacheWorker`, and remove the code from
 `CachedTimelineViewModel`.

- Create the periodic worker in `TuskyApplication`, ensuring that the
  database is only pruned when the device is idle.

app/src/main/java/com/keylesspalace/tusky/di/AppComponent.kt

@@ -34,7 +34,8 @@ import javax.inject.Singleton
         ActivitiesModule::class,
         ServicesModule::class,
         BroadcastReceiverModule::class,
-        ViewModelModule::class
+        ViewModelModule::class,
+        WorkerModule::class
     ]
 )
 interface AppComponent {

app/src/main/java/com/keylesspalace/tusky/di/WorkerModule.kt

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2023 Tusky Contributors
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>.
+ */
+
+package com.keylesspalace.tusky.di
+
+import androidx.work.ListenableWorker
+import com.keylesspalace.tusky.worker.ChildWorkerFactory
+import com.keylesspalace.tusky.worker.NotificationWorker
+import com.keylesspalace.tusky.worker.PruneCacheWorker
+import dagger.Binds
+import dagger.MapKey
+import dagger.Module
+import dagger.multibindings.IntoMap
+import kotlin.reflect.KClass
+
+@Retention(AnnotationRetention.RUNTIME)
+@MapKey
+annotation class WorkerKey(val value: KClass<out ListenableWorker>)
+
+@Module
+abstract class WorkerModule {
+    @Binds
+    @IntoMap
+    @WorkerKey(NotificationWorker::class)
+    internal abstract fun bindNotificationWorkerFactory(worker: NotificationWorker.Factory): ChildWorkerFactory
+
+    @Binds
+    @IntoMap
+    @WorkerKey(PruneCacheWorker::class)
+    internal abstract fun bindPruneCacheWorkerFactory(worker: PruneCacheWorker.Factory): ChildWorkerFactory
+}