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/execution_layer/src/test_utils/handle_rpc.rs

@@ -49,6 +49,12 @@ pub async fn handle_rpc<E: EthSpec>(
                         .latest_execution_block(),
                 )
                 .unwrap()),
+                "0x0" => Ok(serde_json::to_value(
+                    ctx.execution_block_generator
+                        .read()
+                        .genesis_execution_block(),
+                )
+                .unwrap()),
                 other => Err((
                     format!("The tag {} is not supported", other),
                     BAD_PARAMS_ERROR_CODE,