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