feat: enhance Telegram notifications

[Arch0998]

Notification improvements:

• Added a new Celery task notify_successful_payment in notifications/tasks.py to send detailed Telegram notifications when a payment is completed, including user, book, payment amount, type, and status.
• Enhanced the formatting and content of borrowing and overdue notifications in notifications/tasks.py to include user full name, book details, daily fee, and days overdue, using clearer and more informative messages.

Payment processing reliability:

• Updated payment status changes in payments/views.py to use database transactions and row-level locking (select_for_update) for atomicity and consistency. Notifications for successful payments are now triggered only after the status is updated.
• Imported the new notification task into payments/views.py to enable asynchronous notification after payment success.
• Added the transaction import to payments/views.py to support atomic database operations during payment status updates.