Update Simulator tests (#5520)

* Rewrite Simulator

* Add fallback simulator

* Try Sean's test fix

* More fixes

* Cleanup

* Merge branch 'unstable' into update-simulator

* Update cli.rs

* Add sync sim to basic sim

* Formatting

* Add fixes and new block production check

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into update-simulator

* fix compile

beacon_node/client/src/builder.rs

@@ -26,6 +26,7 @@ use eth2::{
     types::{BlockId, StateId},
     BeaconNodeHttpClient, Error as ApiError, Timeouts,
 };
+use execution_layer::test_utils::generate_genesis_header;
 use execution_layer::ExecutionLayer;
 use futures::channel::mpsc::Receiver;
 use genesis::{interop_genesis_state, Eth1GenesisService, DEFAULT_ETH1_BLOCK_HASH};
@@ -267,6 +268,21 @@ where
                 )?;
                 builder.genesis_state(genesis_state).map(|v| (v, None))?
             }
+            ClientGenesis::InteropMerge {
+                validator_count,
+                genesis_time,
+            } => {
+                let execution_payload_header = generate_genesis_header(&spec, true);
+                let keypairs = generate_deterministic_keypairs(validator_count);
+                let genesis_state = interop_genesis_state(
+                    &keypairs,
+                    genesis_time,
+                    Hash256::from_slice(DEFAULT_ETH1_BLOCK_HASH),
+                    execution_payload_header,
+                    &spec,
+                )?;
+                builder.genesis_state(genesis_state).map(|v| (v, None))?
+            }
             ClientGenesis::GenesisState => {
                 info!(
                     context.log(),