In-Memory Database Implementation

Implement an in-memory database task with multiple levels of features. The database supports records identified by string keys, each containing multiple string field-value pairs. Level 1 Basic Operations: set(key, field, value) get(key, field) delete(key, field) Level 2 Adds read-only listing features: scan(key) → returns field(value) list sorted lexicographically scan_by_prefix(key, prefix) → same format, filtered by field prefix Level 3 Introduces timestamps and TTL (Time-To-Live): All operations have _at versions with a timestamp set_at_with_ttl defines a valid interval [timestamp, timestamp + ttl) Expired fields should not appear in get_at, scan_at, or prefix scans Time always moves forward, and tests never mix timestamped and non-timestamped APIs Level 4 Adds backup and restore: backup(timestamp) stores the database state with remaining TTL restore(timestamp, timestamp_to_restore) restores from the latest backup before or at the given time TTL expiration must be recalculated after restore Please implement the features, solve with code, and pass the related tests. Example Input set user1 name Alice get user1 name