feat(scroll): update client (#1603)

- add `scroll-rpc` crate, since `eth_getProof` is slightly different on
scroll and ethers can't handle it
- tbh im probably going to just use our own wrapper around the eth rpc
at this point, building off of this crate. we only need a small subset
of the api and if we plan to support more l2s/eth-ish chains down the
line, it will save a lot of headaches to have it all in-house and fully
customizable to our needs
- abstract a bit more between eth and scroll
- embrace the `BoxDynError``
- add boilerplate for `BatchHeader` which we might need down the line
for tracking timestamps