Support for simple caching

The client should support a simple caching mechanism (not as complex as Apollo client [1], more like a simple default config that improves simple default setups).

TODO: define how this should exactly work

[1]
https://www.apollographql.com/docs/react/data/queries/#supported-fetch-policies https://www.apollographql.com/docs/react/caching/cache-configuration/

首先审查所请求的简单缓存行为，以及链接的 Apollo fetch-policy 和 cache-configuration 参考资料。该 issue 首先需要一份达成一致的设计，明确默认配置、缓存行为和范围；当这些决策被记录为可执行的需求时，工作即告完成。

由索引模型根据 Issue 内容生成。