Optimistic sync spec tests (v1.2.0) (#3564)

## Issue Addressed

Implements new optimistic sync test format from https://github.com/ethereum/consensus-specs/pull/2982.

## Proposed Changes

- Add parsing and runner support for the new test format.
- Extend the mock EL with a set of canned responses keyed by block hash. Although this doubles up on some of the existing functionality I think it's really nice to use compared to the `preloaded_responses` or static responses. I think we could write novel new opt sync tests using these primtives much more easily than the previous ones. Forks are natively supported, and different responses to `forkchoiceUpdated` and `newPayload` are also straight-forward.

## Additional Info

Blocked on merge of the spec PR and release of new test vectors.

beacon_node/execution_layer/src/test_utils/handle_rpc.rs

@@ -77,6 +77,11 @@ pub async fn handle_rpc<T: EthSpec>(
         ENGINE_NEW_PAYLOAD_V1 => {
             let request: JsonExecutionPayloadV1<T> = get_param(params, 0)?;
 
+            // Canned responses set by block hash take priority.
+            if let Some(status) = ctx.get_new_payload_status(&request.block_hash) {
+                return Ok(serde_json::to_value(JsonPayloadStatusV1::from(status)).unwrap());
+            }
+
             let (static_response, should_import) =
                 if let Some(mut response) = ctx.static_new_payload_response.lock().clone() {
                     if response.status.status == PayloadStatusV1Status::Valid {
@@ -120,6 +125,15 @@ pub async fn handle_rpc<T: EthSpec>(
 
             let head_block_hash = forkchoice_state.head_block_hash;
 
+            // Canned responses set by block hash take priority.
+            if let Some(status) = ctx.get_fcu_payload_status(&head_block_hash) {
+                let response = JsonForkchoiceUpdatedV1Response {
+                    payload_status: JsonPayloadStatusV1::from(status),
+                    payload_id: None,
+                };
+                return Ok(serde_json::to_value(response).unwrap());
+            }
+
             let mut response = ctx
                 .execution_block_generator
                 .write()