Fix Rust beta compiler errors (1.77) (#5180)

* Lint fixes

* More fixes for beta compiler.

* Format fixes

* Move `#[allow(dead_code)]` to field level.

* Remove old comment.

* Update beacon_node/execution_layer/src/test_utils/mod.rs

Co-authored-by: João Oliveira <hello@jxs.pt>

* remove duplicate line

beacon_node/beacon_chain/src/state_advance_timer.rs

@@ -51,7 +51,8 @@ const MAX_BLOCK_PRODUCTION_CACHE_DISTANCE: u64 = 4;
 #[derive(Debug)]
 enum Error {
     BeaconChain(BeaconChainError),
-    HeadMissingFromSnapshotCache(Hash256),
+    // We don't use the inner value directly, but it's used in the Debug impl.
+    HeadMissingFromSnapshotCache(#[allow(dead_code)] Hash256),
     MaxDistanceExceeded {
         current_slot: Slot,
         head_slot: Slot,