Implement a versioned in-memory DB with CAS and history

Implement an in-memory key-field store. Each record is identified by a pair (key, field) and stores the following: value expire_at — an integer timestamp; the special value +Infinity means the record never expires. A record is visible at time t exactly when t is strictly less than expire_at. Every operation receives a timestamp, and you may assume timestamps arrive in non-decreasing order. The store must also support historical reads: given an earlier time, return the value…