Local Notifications for Timers (Ongoing & End Notifications) Fixes #519

This pull request adds a new feature that utilizes local notifications to enhance the timer experience:

End Notifications: Users are now notified when a timer finishes, even if the app is closed. This ensures they don't miss important alarms or reminders.
Ongoing Notifications: While a timer is active, an ongoing notification displays the remaining time in the notification bar. This allows users to easily track time at a glance.

Fixes #(519)