backdateLastActivity static method
Moves the last-activity time by into the past. Past 30 minutes, the
next launch starts a new session.
Implementation
static Future<void> backdateLastActivity(Duration by) async {
final storage = await _storage();
storage.setItem(
SessionKeys.lastActivity,
'${systemClock() - by.inMilliseconds}',
);
await storage.flushWrites();
}