Move cache management to a dedicated class and in the setting module, for clarity.

features/preferences/api/src/main/kotlin/io/element/android/features/preferences/api/CacheService.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.element.android.features.preferences.api
+
+import kotlinx.coroutines.flow.Flow
+
+interface CacheService {
+    /**
+     * Returns a flow of the current cache index, can let the app to know when the
+     * cache has been cleared, for instance to restart the app.
+     * Will be a flow of Int, starting from 0, and incrementing each time the cache is cleared.
+     */
+    fun cacheIndex(): Flow<Int>
+}