create unified slashing cache (#5033)

* create unified slashing cache

* add observed slashable file

* fix broadcast validation tests

* revert block seen cache changes

* clean up slashable cache test

* check header signatures for RPC blobs

* don't throw error on RPC signature invalie

beacon_node/beacon_chain/src/blob_verification.rs

@@ -599,6 +599,16 @@ pub fn validate_blob_sidecar_for_gossip<T: BeaconChainTypes>(
         });
     }
 
+    chain
+        .observed_slashable
+        .write()
+        .observe_slashable(
+            blob_sidecar.slot(),
+            blob_sidecar.block_proposer_index(),
+            block_root,
+        )
+        .map_err(|e| GossipBlobError::BeaconChainError(e.into()))?;
+
     // Now the signature is valid, store the proposal so we don't accept another blob sidecar
     // with the same `BlobIdentifier`.
     // It's important to double-check that the proposer still hasn't been observed so we don't