Fix the dependency of ether-rs

[noel2004]

Ether-rs has been published to crate.io and the current version is 0.6.1. Should we drop the dependency from git branch to make the dependency stable?

And maybe we could consider re-exporting ether-rs so the downstream package (like rollup-state-manager) do not need to include ethere-rs in their dependencies any more.

[0xmountaintop]

good idea