Add broadcast validation routes to Beacon Node HTTP API (#4316)

## Issue Addressed

 - #4293 
 - #4264 

## Proposed Changes

*Changes largely follow those suggested in the main issue*.

 - Add new routes to HTTP API
   - `post_beacon_blocks_v2`
   - `post_blinded_beacon_blocks_v2`
 - Add new routes to `BeaconNodeHttpClient`
   - `post_beacon_blocks_v2`
   - `post_blinded_beacon_blocks_v2`
 - Define new Eth2 common types
   - `BroadcastValidation`, enum representing the level of validation to apply to blocks prior to broadcast
   - `BroadcastValidationQuery`, the corresponding HTTP query string type for the above type
 - ~~Define `_checked` variants of both `publish_block` and `publish_blinded_block` that enforce a validation level at a type level~~
 - Add interactive tests to the `bn_http_api_tests` test target covering each validation level (to their own test module, `broadcast_validation_tests`)
   - `beacon/blocks`
       - `broadcast_validation=gossip`
         - Invalid (400)
         - Full Pass (200)
         - Partial Pass (202)
        - `broadcast_validation=consensus`
          - Invalid (400)
          - Only gossip (400)
          - Only consensus pass (i.e., equivocates) (200)
          - Full pass (200)
        - `broadcast_validation=consensus_and_equivocation`
          - Invalid (400)
          - Invalid due to early equivocation (400)
          - Only gossip (400)
          - Only consensus (400)
          - Pass (200)
   - `beacon/blinded_blocks`
       - `broadcast_validation=gossip`
         - Invalid (400)
         - Full Pass (200)
         - Partial Pass (202)
        - `broadcast_validation=consensus`
          - Invalid (400)
          - Only gossip (400)
          - ~~Only consensus pass (i.e., equivocates) (200)~~
          - Full pass (200)
        - `broadcast_validation=consensus_and_equivocation`
          - Invalid (400)
          - Invalid due to early equivocation (400)
          - Only gossip (400)
          - Only consensus (400)
          - Pass (200)
 - Add a new trait, `IntoGossipVerifiedBlock`, which allows type-level guarantees to be made as to gossip validity
 - Modify the structure of the `ObservedBlockProducers` cache from a `(slot, validator_index)` mapping to a `((slot, validator_index), block_root)` mapping
 - Modify `ObservedBlockProducers::proposer_has_been_observed` to return a `SeenBlock` rather than a boolean on success
 - Punish gossip peer (low) for submitting equivocating blocks
 - Rename `BlockError::SlashablePublish` to `BlockError::SlashableProposal`

## Additional Info

This PR contains changes that directly modify how blocks are verified within the client. For more context, consult [comments in-thread](https://github.com/sigp/lighthouse/pull/4316#discussion_r1234724202).


Co-authored-by: Michael Sproul <michael@sigmaprime.io>

beacon_node/http_api/tests/main.rs

@@ -1,5 +1,6 @@
 #![cfg(not(debug_assertions))] // Tests are too slow in debug.
 
+pub mod broadcast_validation_tests;
 pub mod fork_tests;
 pub mod interactive_tests;
 pub mod status_tests;

beacon_node/http_api/tests/tests.rs

@@ -159,7 +159,7 @@ impl ApiTester {
 
         // `make_block` adds random graffiti, so this will produce an alternate block
         let (reorg_block, _reorg_state) = harness
-            .make_block(head.beacon_state.clone(), harness.chain.slot().unwrap())
+            .make_block(head.beacon_state.clone(), harness.chain.slot().unwrap() + 1)
             .await;
 
         let head_state_root = head.beacon_state_root();
@@ -1248,14 +1248,23 @@ impl ApiTester {
     }
 
     pub async fn test_post_beacon_blocks_invalid(mut self) -> Self {
-        let mut next_block = self.next_block.clone();
-        *next_block.message_mut().proposer_index_mut() += 1;
+        let block = self
+            .harness
+            .make_block_with_modifier(
+                self.harness.get_current_state(),
+                self.harness.get_current_slot(),
+                |b| {
+                    *b.state_root_mut() = Hash256::zero();
+                },
+            )
+            .await
+            .0;
 
-        assert!(self.client.post_beacon_blocks(&next_block).await.is_err());
+        assert!(self.client.post_beacon_blocks(&block).await.is_err());
 
         assert!(
             self.network_rx.network_recv.recv().await.is_some(),
-            "invalid blocks should be sent to network"
+            "gossip valid blocks should be sent to network"
         );
 
         self
@@ -4126,7 +4135,7 @@ impl ApiTester {
             .unwrap();
 
         let expected_reorg = EventKind::ChainReorg(SseChainReorg {
-            slot: self.next_block.slot(),
+            slot: self.reorg_block.slot(),
             depth: 1,
             old_head_block: self.next_block.canonical_root(),
             old_head_state: self.next_block.state_root(),
@@ -4136,6 +4145,8 @@ impl ApiTester {
             execution_optimistic: false,
         });
 
+        self.harness.advance_slot();
+
         self.client
             .post_beacon_blocks(&self.reorg_block)
             .await