feat: implement eth_getFilterChanges

[ncitron]

We removed support for eth_getFilterChanges in #608. In this PR we removed a lot of RPC dependencies which are not needed, such as using RPC filters for things, instead relying on replicating the functionality entirely within helios. We should be able to get eth_getFilterChanges working using the same techniques as we did for eth_getFilterLogs.

[ncitron]

GitHub won't let me assign for some reason but @varun-doshi is working on this.

[hawkadrian]

Hi @ncitron

I noticed there's no update in this issue so I decided to pick it up and implement changes, it'd be nice if you have a look at it some time :)