Is your feature request related to a problem? Please describe.
Isthmus is the upcoming OP-stack hardfork which introduces breaking changes to how the Execution Layer component should behave. A general overview of these changes can be read in the official OP-stack spec: https://specs.optimism.io/protocol/isthmus/exec-engine.html

Describe the solution you'd like
Nethermind should make the required changes to its Optimism plugin in order to be properly compliant with the latest hardfork.

Describe alternatives you've considered
The only option besides actually implementing the hardfork is dropping support for OP-stack chains. We won't go down this route.

Additional context
Isthmus includes the following features:

Operator fee

• Spec: https://github.com/ethereum-optimism/design-docs/blob/b807dc5880f48a3631222e7f519c02a7668f2493/protocol/operator-fee.md
• Spec PR: Isthmus: operator fee  ethereum-optimism/specs#382
• OP-geth: isthmus: operator fee ethereum-optimism/op-geth#388
• OP-node & contracts: isthmus: operator fee ethereum-optimism/optimism#12166 (these are non EL changes so we should be able to ignore them)

L2 Withdrawal roots in Block Header

• OP-geth: Isthmus: re-introduce withdrawals root in block header ethereum-optimism/op-geth#451
• OP-geth (fix): feat: ensure requests array empty post-Isthmus ethereum-optimism/op-geth#478

As for timeline, Isthmus is supposed to:

• Launch on Testnet (Sepolia) on March 26
• Launch on Mainnet on April 16