Implement engine API v1.0.0-alpha.4 (#2810)

* Added ForkchoiceUpdatedV1 & GetPayloadV1

* Added ExecutePayloadV1

* Added new geth test vectors

* Separated Json Object/Serialization Code into file

* Deleted code/tests for Requests Removed from spec

* Finally fixed serialization of null '0x'

* Made Naming of JSON Structs Consistent

* Fix clippy lints

* Remove u64 payload id

* Remove unused serde impls

* Swap to [u8; 8] for payload id

* Tidy

* Adjust some block gen return vals

* Tidy

* Add fallback when payload id is unknown

* Remove comment

Co-authored-by: Mark Mackey <mark@sigmaprime.io>

consensus/proto_array/src/proto_array_fork_choice.rs

@@ -40,6 +40,15 @@ impl ExecutionStatus {
     pub fn irrelevant() -> Self {
         ExecutionStatus::Irrelevant(false)
     }
+
+    pub fn block_hash(&self) -> Option<Hash256> {
+        match self {
+            ExecutionStatus::Valid(hash)
+            | ExecutionStatus::Invalid(hash)
+            | ExecutionStatus::Unknown(hash) => Some(*hash),
+            ExecutionStatus::Irrelevant(_) => None,
+        }
+    }
 }
 
 /// A block that is to be applied to the fork choice.