Builder Specs v0.2.0 (#3134)

## Issue Addressed

https://github.com/sigp/lighthouse/issues/3091

Extends https://github.com/sigp/lighthouse/pull/3062, adding pre-bellatrix block support on blinded endpoints and allowing the normal proposal flow (local payload construction) on blinded endpoints. This resulted in better fallback logic because the VC will not have to switch endpoints on failure in the BN <> Builder API, the BN can just fallback immediately and without repeating block processing that it shouldn't need to. We can also keep VC fallback from the VC<>BN API's blinded endpoint to full endpoint.

## Proposed Changes

- Pre-bellatrix blocks on blinded endpoints
- Add a new `PayloadCache` to the execution layer
- Better fallback-from-builder logic

## Todos

- [x] Remove VC transition logic
- [x] Add logic to only enable builder flow after Merge transition finalization
- [x] Tests
- [x] Fix metrics
- [x] Rustdocs


Co-authored-by: Mac L <mjladson@pm.me>
Co-authored-by: realbigsean <sean@sigmaprime.io>

beacon_node/beacon_chain/src/test_utils.rs

@@ -14,7 +14,9 @@ use bls::get_withdrawal_credentials;
 use execution_layer::test_utils::DEFAULT_JWT_SECRET;
 use execution_layer::{
     auth::JwtKey,
-    test_utils::{ExecutionBlockGenerator, MockExecutionLayer, DEFAULT_TERMINAL_BLOCK},
+    test_utils::{
+        ExecutionBlockGenerator, MockExecutionLayer, TestingBuilder, DEFAULT_TERMINAL_BLOCK,
+    },
     ExecutionLayer,
 };
 use fork_choice::CountUnrealized;
@@ -154,6 +156,7 @@ pub struct Builder<T: BeaconChainTypes> {
     store_mutator: Option<BoxedMutator<T::EthSpec, T::HotStore, T::ColdStore>>,
     execution_layer: Option<ExecutionLayer<T::EthSpec>>,
     mock_execution_layer: Option<MockExecutionLayer<T::EthSpec>>,
+    mock_builder: Option<TestingBuilder<T::EthSpec>>,
     runtime: TestRuntime,
     log: Logger,
 }
@@ -285,6 +288,7 @@ where
             store_mutator: None,
             execution_layer: None,
             mock_execution_layer: None,
+            mock_builder: None,
             runtime,
             log,
         }
@@ -388,6 +392,38 @@ where
         self
     }
 
+    pub fn mock_execution_layer_with_builder(mut self, beacon_url: SensitiveUrl) -> Self {
+        // Get a random unused port
+        let port = unused_port::unused_tcp_port().unwrap();
+        let builder_url = SensitiveUrl::parse(format!("http://127.0.0.1:{port}").as_str()).unwrap();
+
+        let spec = self.spec.clone().expect("cannot build without spec");
+        let mock_el = MockExecutionLayer::new(
+            self.runtime.task_executor.clone(),
+            spec.terminal_total_difficulty,
+            DEFAULT_TERMINAL_BLOCK,
+            spec.terminal_block_hash,
+            spec.terminal_block_hash_activation_epoch,
+            Some(JwtKey::from_slice(&DEFAULT_JWT_SECRET).unwrap()),
+            Some(builder_url.clone()),
+        )
+        .move_to_terminal_block();
+
+        let mock_el_url = SensitiveUrl::parse(mock_el.server.url().as_str()).unwrap();
+
+        self.mock_builder = Some(TestingBuilder::new(
+            mock_el_url,
+            builder_url,
+            beacon_url,
+            spec,
+            self.runtime.task_executor.clone(),
+        ));
+        self.execution_layer = Some(mock_el.el.clone());
+        self.mock_execution_layer = Some(mock_el);
+
+        self
+    }
+
     /// Instruct the mock execution engine to always return a "valid" response to any payload it is
     /// asked to execute.
     pub fn mock_execution_layer_all_payloads_valid(self) -> Self {
@@ -456,6 +492,7 @@ where
             shutdown_receiver: Arc::new(Mutex::new(shutdown_receiver)),
             runtime: self.runtime,
             mock_execution_layer: self.mock_execution_layer,
+            mock_builder: self.mock_builder.map(Arc::new),
             rng: make_rng(),
         }
     }
@@ -474,6 +511,7 @@ pub struct BeaconChainHarness<T: BeaconChainTypes> {
     pub runtime: TestRuntime,
 
     pub mock_execution_layer: Option<MockExecutionLayer<T::EthSpec>>,
+    pub mock_builder: Option<Arc<TestingBuilder<T::EthSpec>>>,
 
     pub rng: Mutex<StdRng>,
 }