Partial Incompatibility with Blockscout

[ckoopmann]

While trying to implement a cast command to migrate a contract verification from on explorer to another (specifically from etherscan to blockscout), I encountered the issue that the contract_source_code and submit_contract_verification methods fail when run against blockscout. (more specifically against "https://eth.blockscout.com/api".

I created tests reproducing the issue for contract_source_code and submit_contract_verification.

Judging from the error messages (see screenshots), the former issue seems to be a pretty strait forward deserialziation issue whereas the latter has a pretty cryptic error message.