Add normalized event caching

[ryangoree]

Events are currently cached by their request parameters. Overlapping block ranges are considered separate cache entries resulting in the same event being cached multiple times if fetched with different parameters.

Ideally the cache would be aware of the range of events already cached and only fetch ranges it hasn't fetched yet, managing a single cached list of events for each event type.

https://hackmd.io/k90EXlNhRfGujuQgyb_hoQ

[ryangoree]

I've got a working example script on the normalized-event-cache branch that implements the initial 3 store design, but it's pretty convoluted. I'll need to do more testing to verify the benefits and think about how it fits into the existing cache design.

Original 3 store design in the hackmd above: