Fetch State
data class FetchState<TData>(var loading: Boolean? = null, var params: TParams? = null, var data: TData? = null, var error: Throwable? = null) : IFetchStata<TData> , Copyable<FetchState<TData>>
Fetch 类持有数据的内部状态
Fetch 类持有数据的内部状态