Design an in-memory LRU cache and explain how to extend it with TTL support. Requirements: - `get(key)` returns the value if the key exists and has not expired; otherwise it returns a cache miss. - `put(key, value, ttl)` inserts or updates an entry with an expiration time. - When capacity is exceeded, evict the least recently used item. - Expired items should never be returned, and the design should explain how they are removed. - Discuss the data structures, time complexity, cleanup strategy, and concurrency considerations.