Add Ethereum Signature Verification

[pscott]

This PR:

• Adds the EthSig.cairo authenticator which verifies a classic Ethereum signature (r, s, v) over an EIP-712 hash (hashes types are in tests/starknet/helper/types.ts).
• Modifies felt_to_uint256 to use split_felt from the common library

Note: metadataURI is NOT added to the Propose type because strings are a little bit hash in Cairo. This should come in a later update :) (tracking issue: #202)

Closes #30 !! 🥳

[pscott]

@Orland0x wtf test is failing in the StorageProof side of things? Any idea of what's going on here? I guess it has to do with a cairo version maybe?

https://github.com/snapshot-labs/sx-core/runs/7044640255?check_suite_focus=true

[Orland0x]

Hmmm 0x3ae0... is the selector for get_latest_l1_block in Fossil so I think its to do with the an old version of Fossil (that didnt have that method) getting deployed.
try adding git submodule update --remote to the GA