fix: Restoring backup from file doesn't respect 'swipe actions' setting

[shamim-emon]

• fixes [k-9 mail] restoring backup from file doesn't respect 'swipe actions' setting #10621

🐛 Problem

• While restoring backup from files , GeneralSettingsWriter uses legacy preference system to store GeneralSettings values.
• New PreferenceManagers for GeneralSettings don't listen to this update and so GeneralSettings flow does not react to this change and UI does not get update without restarting the app.

🛠️ Solution

• Made all preferenceManagers subscribe to PreferenceChangeBroker.
• Notify all preferenceManagers upon GeneralSetting restore on GeneralSettingsWriter.

[wmontwe]

Using the PreferenceChangeBroker solved the issue, but it causes side effects.

This is using a simple broadcaster that notifies all subscribers and therefore could lead to a broadcast storm as now every settings related manager reacts to any change. Just add a log to every receive and then change the "animation" setting you will see 11 managers updating.

While the individual reloads are relatively small, they quickly add up causing simultaneous updates across multiple managers that end up aggregated as GeneralSettings with multiple updates to consumers in the app.

Some ideas:

These are rough ideas and maybe not doable or adding to much complexity.

1. Keep the change broker, but scope the emissions (adds complexity)

enum class PreferenceScope { ALL, DISPLAY, PRIVACY, NETWORK, DEBUGGING }

interface PreferenceChangePublisher {
    fun publish(scope: PreferenceScope = PreferenceScope.ALL)
}

fun interface PreferenceChangeSubscriber {
    fun receive(scope: PreferenceScope)
}

// In a manager:
override fun receive(scope: PreferenceScope) {
    if (scope == PreferenceScope.ALL || scope == PreferenceScope.PRIVACY) {
        configState.update { loadConfig() }
    }
}

2. Use key-based notifications

fun interface PreferenceChangeSubscriber {
    fun receive(changedKey: String)
}

// In a manager:
override fun receive(changedKey: String) {
    if (myOwnedKeys.contains(changedKey)) {
        configState.update { loadConfig() }
    }
}

3. Use a reactive storage

class DefaultNotificationPreferenceManager(...) {
    val configFlow = combine(
        storage.observeBoolean(KEY_QUIET_TIME),
        storage.observeString(KEY_NOTIFICATION_VIBRATE)
    ) { quietTime, vibrate -> 
        NotificationSettings(quietTime, vibrate) 
    }.stateIn(scope, Eagerly, initialValue)
}

But our storage is not reactive yet.

---

Other ideas are welcome

[github-actions]

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