Memory adapter

MemoryAdapter keeps named saves in a Map in the current process. It is useful for tests and short-lived workflows:

import { MemoryAdapter } from "./core/storage/MemoryAdapter.js";

const storage = new MemoryAdapter();
engine.useStorage(storage);
await engine.persist("test-save");

Data is lost when the process exits. The adapter has a clear() helper for test isolation and provides no durability, cross-process sharing, or backup.