Total difficulty is removed from block responses

[agostbiro]

A recent change to the Ethereum execution API schema removed totalDifficulty from eth_getBlockByNumber and eth_getBlockByHash responses. Geth has implemented this change and it caused panics in EDR when it didn't receive the expecrted totalDifficulty field from Geth nodes. We should probably adapt this change, but we should figure out first if it'll break any projects depending on Hardhat/EDR. In the meantime we fall back to the terminal total difficulty in EDR if the remote doesn't return a total difficulty.

Definition of Done

• Temp fix: fix: total difficulty fallback for remote blocks #697
• Fix the TODOs referencing this issue in the code base
• TBD