Implement KV Store and Token Bucket

The coding portion covered two implementation tasks: 1. Implement a simple in-memory key-value store. Support basic operations such as: - `put(key, value)`: insert or update a value - `get(key)`: return the current value or indicate that the key does not exist - `delete(key)`: remove a key Be prepared to discuss API design, edge cases, and expected time complexity. 2. Implement a concurrent token-bucket rate limiter. The bucket has: - a fixed maximum capacity - a refill rate of `r` tokens per second - an operation such as `allow(n)` that consumes `n` tokens if enough tokens are available, otherwise rejects the request Your implementation should be thread-safe under concurrent callers, refill tokens based on elapsed time, and never allow the token count to exceed capacity. Explain your synchronization strategy and complexity.