Crash ExEx task when the ExEx future returns

[onbjerg]

Describe the feature

If an ExEx future returns it means it has stopped processing incoming notifications which we will (at least for now) treat as a fatal error. We assume that users running ExEx's want them to be up to date, and we have built the system under this assumption.

Because of this, we should panic here even if the ExEx returns Ok(()):

reth/crates/node-builder/src/builder.rs

Lines 630 to 631 in 4d79967

	exex.await.unwrap_or_else(|_| panic!("exex {} crashed", id))
	});

Additional context

No response