workflow - StateRepository 状态持久化

StateRepository 接口，状态仓库接口。提供流程节点状态的持久化支持。内置实现有：

• InMemoryStateRepository，内存适配的状态仓库
• RedisStateRepository，Redis 适配的状态仓库

1、StateRepository 使用示例

WorkflowExecutor work = WorkflowExecutor.of(engine,
                new ActorStateController(), 
                new InMemoryStateRepository()); 

FlowContext context = FlowContext.of("i1").put("actor", "@admin");
Graph graph = engine.getGraph("g1");

//1. 认领任务
Task task = work.claimTask(graph, context);

//2. 提交任务
work.submitTask(task, TaskAction.FORWARD, context);

2、StateRepository 接口字典（定制参考）

public interface StateRepository {
    /**
     * 状态获取
     */
    StateType stateGet(FlowContext context, Node node);

    /**
     * 状态推入
     */
    void statePut(FlowContext context, Node node, StateType state);

    /**
     * 状态移除
     */
    void stateRemove(FlowContext context, Node node);

    /**
     * 状态清空
     */
    void stateClear(FlowContext context);
}