Design In-Memory Database with Backup

Implement a simplified in-memory database with TTL and backup/restore functionality.

Level 1 - Basic Operations:

• setData(key, field, value) - Set field-value pair for key
• getData(key, field) - Get value, return "" if not exists
• deleteData(key, field) - Delete field, return true if existed

Level 2 - Scan Operation:

• scanData(key) - Return all "field(value)" pairs, sorted alphabetically

Level 3 - TTL (Time-To-Live):

• setDataWithTTL(key, field, value, timestamp, ttl) - Set with expiration at timestamp + ttl
• Expired data should not be returned

Level 4 - Backup and Restore:

• backup(timestamp) - Save database state, return count of non-empty records
• restore(timestamp, backupTimestamp) - Restore from backup, recalculate TTLs based on remaining time