Add BeaconChainHarness tests for The Merge (#2661)

* Start adding merge tests

* Expose MockExecutionLayer

* Add mock_execution_layer to BeaconChainHarness

* Progress with merge test

* Return more detailed errors with gas limit issues

* Use a better gas limit in block gen

* Ensure TTD is met in block gen

* Fix basic_merge tests

* Start geth testing

* Fix conflicts after rebase

* Remove geth tests

* Improve merge test

* Address clippy lints

* Make pow block gen a pure function

* Add working new test, breaking existing test

* Fix test names

* Add should_panic

* Don't run merge tests in debug

* Detect a tokio runtime when starting MockServer

* Fix clippy lint, include merge tests

beacon_node/execution_layer/Cargo.toml

@@ -27,3 +27,4 @@ lru = "0.6.0"
 exit-future = "0.2.0"
 tree_hash = { path = "../../consensus/tree_hash"}
 tree_hash_derive = { path = "../../consensus/tree_hash_derive"}
+parking_lot = "0.11.0"