fix(notification): cancel() crashes on Android with empty notifications list (fix #2341)

[avebeatrix]

Fixes #2341 (the cancelAll() part — other items in that issue are unaddressed by this PR).

Problem

NotificationPlugin.kt:42 declares the cancel-command argument shape as:

@InvokeArg
class CancelArgs {
  lateinit var notifications: List<Int>
}

The handler then unconditionally reads args.notifications and forwards it to manager.cancel(...). Both supported callers of "cancel all" hit this dead-end:

• JS cancelAll() from @tauri-apps/plugin-notification invokes plugin:notification|cancel with no notifications field.
• Rust SDK NotificationExt::cancel_all() (mobile.rs) does run_mobile_plugin("cancel", ()) — same effect.

In both cases Kotlin throws UninitializedPropertyAccessException when the handler reads args.notifications. On the JS side this bubbles up as a rejected invoke() promise that the sendNotification polyfill silently drops, so callers see no notifications cancelled and no error.

This was observed downstream while shipping a reminder-style notification feature — debugging required tracing through the Rust SDK, the plugin's Android Kotlin, and finally dumpsys alarm to confirm that the schedule loop was being aborted by the failing cancelAll() before any notify call ever ran.

Fix

Three small changes, all in plugins/notification/android/src/main/java/:

1. NotificationPlugin.kt — CancelArgs.notifications is now var notifications: List<Int> = listOf() (optional, defaults to empty). The handler routes an empty list through a new manager.cancelAll(); non-empty still goes through the existing manager.cancel(ids).

2. TauriNotificationManager.kt — new cancelAll() method that enumerates saved IDs via the existing NotificationStorage.getSavedNotificationIds() and reuses the existing per-id cancel() cleanup path (dismiss visible + cancel timer + delete storage entry). No duplicated cleanup logic.

3. .changes/notification-cancel-all-android.md — patch bump on both notification and notification-js per the repo .changes/readme.md rule («both packages need to be bumped with the same increment even when only one side changed»).

Tests

The plugin's plugins/notification/android/src/test/ currently contains only the placeholder ExampleUnitTest.kt — there is no existing scaffold for handler/manager unit tests. I deliberately did not add a one-off test in this PR so the change stays minimal; happy to add a focused test for cancel(empty) if maintainers want the coverage and can confirm a preferred mocking approach for Invoke / manager.

Compatibility

• JS cancelAll(): starts working as documented.
• JS cancel([1, 2, 3]): unchanged — still routed through manager.cancel(ids).
• Rust NotificationExt::cancel_all(): starts working.
• Rust NotificationExt::cancel(vec![1, 2, 3]): unchanged.
• iOS / desktop: untouched (Android-only change).

No public API change. No migration needed.