Implement a persistent sharded key-value store

## Problem Implement a simple **key–value store** that persists data on disk. You must store the data in **fixed-size shards**, where each shard is saved in **one file**. If a shard file reaches its maximum size, new writes must go into a **new shard file**. The store must support **shutdown (persist)** and **restore (recover)**. You are given helper functions: - `encode(key, value) -> bytes` to serialize a key/value record - `decode(bytes) -> (key, value)` to deserialize a record Assume keys and values are strings (or byte arrays), and `encode/decode` are inverses for valid records. ## Required API Design and implement (language-agnostic) functions/methods equivalent to: - `put(key, value)` - Insert or overwrite the value for `key`. - `get(key) -> value | null` - Return the current value for `key`, or `null`/`None` if missing. - `delete(key)` (optional if you want to support removals) - Remove `key` if it exists. - `shutdown()` - Ensure all in-memory state is persisted so the store can be restored later. - `restore(directory_path)` (or constructor-based restore) - Load persisted data from disk and make the store usable again. ## Storage requirements - Data is stored across **one or more files** in a directory. - Each file is a **shard** with a configurable maximum size `SHARD_SIZE_BYTES`. - Writes append records to the current shard until it would exceed the shard size; then create a new shard file. ## What to discuss / clarify - Your on-disk layout (file naming, record boundaries, handling partial/corrupt tail). - How you locate the latest value for a key after many overwrites. - What metadata or in-memory index (if any) you maintain. - Complexity of `put/get` and `restore`. - Edge cases: empty store, large values, shard rollover, overwrite semantics, optional delete semantics.