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/src/engine_api.rs

@@ -107,7 +107,9 @@ pub enum BlockByNumberQuery<'a> {
 #[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct ExecutionBlock {
+    #[serde(rename = "hash")]
     pub block_hash: Hash256,
+    #[serde(rename = "number", with = "eth2_serde_utils::u64_hex_be")]
     pub block_number: u64,
     pub parent_hash: Hash256,
     pub total_difficulty: Uint256,