[query] Cache star counts and Whiskers statuses

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The easiest way to do this is to support storing any serde_json::Value, so strings (the current implementation) as well as arrays and objects, etc. I cannot figure out how to get my cache methods to support JSON value generics -- something like cache.get_or<String>(...); where the String type parameter would be the return type and what the value is deserialized to. But currently not possible AFAIK.