Implement an in-memory TTL cache (optionally LRU)

Problem: Implement an in-memory TTL cache (optionally LRU) Implement an in-memory TTLCache that supports per-key expiration (TTL) and returns None for expired items. Required APIs set(key: str, value: str, ttl_ms: int, now_ms: int) -> None Store key=value at now_ms with expiration at now_ms + ttl_ms. get(key: str, now_ms: int) -> Optional[str] Return value if present and not expired; otherwise None. delete(key: str) -> None Optional extensions: Add capacity and evict by LRU when exceeding capacity. Add cleanup(now_ms) to proactively remove expired items. Make it thread-safe using Lock/RLock. Constraints ttl_ms can be 0 (immediate expiry). Re-setting the same key overwrites both value and ttl. Example set("a","x", 100, 0) get("a", 50) → "x" get("a", 150) → None Implement it and include tests for edge cases. Example Input set a x 100 0 get a 50 get a 150 Output x None