Add Gloas EF test infrastructure and fork choice exclusion.

- Add fork choice constants to consts.rs (PayloadStatus, timeliness indices)
- Add payload_timely_threshold() helper to EthSpec
- Exclude Gloas from fork_choice tests until implementation is complete
- Add PayloadAttestation operation test handler for EF tests

testing/ef_tests/tests/tests.rs

@@ -118,6 +118,12 @@ fn operations_bls_to_execution_change() {
     OperationsHandler::<MainnetEthSpec, SignedBlsToExecutionChange>::default().run();
 }
 
+#[test]
+fn operations_payload_attestation() {
+    OperationsHandler::<MinimalEthSpec, PayloadAttestation<_>>::default().run();
+    OperationsHandler::<MainnetEthSpec, PayloadAttestation<_>>::default().run();
+}
+
 #[test]
 fn sanity_blocks() {
     SanityBlocksHandler::<MinimalEthSpec>::default().run();