Allow string | number ids in NotificationsOptions

[BobMakhlin]

This update extends the id property in NotificationsOptions from number to string | number.
It allows applications that use string-based identifiers (such as UUIDs, database keys, or prefixed IDs) to manage notifications programmatically without type casting or conversion.

Rationale:

• Some applications naturally use string IDs for entities and notifications.
• The current numeric-only type requires unnecessary conversions and limits flexibility.
• The internal implementation only compares IDs via strict equality (===), so supporting both types introduces no behavior change or compatibility issues.

Impact:
✅ Backward-compatible: existing numeric IDs continue to work.
✅ No runtime logic changes: ID handling remains equality-based.
✅ Documentation updated accordingly.

Example usage:

notify({ id: 123, text: 'Numeric ID example' });
notify({ id: 'uuid-123', text: 'String ID example' });
notify.close('uuid-123');

@kyvg

[kyvg]

Hi @BobMakhlin, thank you for your pull request! I've already published your changes in 3.4.2 version