chore(engine): simplify StateRootTask creation and hook management

[fgimenez]

Towards #12639

Moves StateRootTask's message channel and hook closure creation inside the type, making it easier to manage externally.

Before:

let (state_root_tx, state_root_rx) = std::sync::mpsc::channel();
let state_root_config = StateRootConfig { consistent_view, input: Arc::new(input) };
let state_root_task =
            StateRootTask::new(state_root_config, state_root_tx.clone(), state_root_rx);
let state_root_handle = state_root_task.spawn();
let state_hook_sender = StateHookSender::new(state_root_tx);
let state_hook = move |state: &EvmState| {
    let _ = state_hook_sender.send(StateRootMessage::StateUpdate(state.clone()));
};
let output = self.metrics.executor.execute_metered(
   executor,
   (&block, U256::MAX).into(),
   Box::new(state_hook),
)?;

After:

let state_root_config = StateRootConfig { consistent_view, input: Arc::new(input) };
let state_root_task =StateRootTask::new(state_root_config);
let state_hook = state_root_task.state_hook();
let state_root_handle = state_root_task.spawn();
let output = self.metrics.executor.execute_metered(
   executor,
   (&block, U256::MAX).into(),
   Box::new(state_hook),
)?;