Implement System Ringtone Support for Alarm Clock

[mahendra-918]

Description

This PR adds support for using system ringtones as alarm sounds in the Ultimate Alarm Clock app.

Proposed Changes

Added platform channel communication to access device's system ringtones Implemented proper storage and retrieval of system ringtone references Created UI for browsing and selecting system ringtones by category (alarms, notifications, ringtones) Added playback mechanisms for preview and alarm activation Optimized caching for faster ringtone loading Improved audio handling with proper session management

Fixes #775

Screenshots

https://github.com/user-attachments/assets/3124fc25-47b9-41d2-8abf-e2add8839bcc

Checklist

• [x] Tests have been added or updated to cover the changes
• [x] Documentation has been updated to reflect the changes
• [x] Code follows the established coding style guidelines
• [x] All tests are passing