core/aggsigdb: refactor MemDB (#2950)

Introduce MemDBV2: instead of relying on a complex system based on channels and read/write queries, simply store objects in a `sync/map`.

Simpler to read and potentially faster in systems in which there's a high rate of goroutine contention.

Add the `aggsigdb_v2` feature flag to enable/disable this feature.

category: refactor
ticket: #1951  
feature_flag: aggsigdb_v2

app/app.go

@@ -465,7 +465,12 @@ func wireCoreWorkflow(ctx context.Context, life *lifecycle.Manager, conf Config,
 		return err
 	}
 
-	aggSigDB := aggsigdb.NewMemDB(deadlinerFunc("aggsigdb"))
+	var aggSigDB core.AggSigDB
+	if featureset.Enabled(featureset.AggSigDBV2) {
+		aggSigDB = aggsigdb.NewMemDBV2(deadlinerFunc("aggsigdb"))
+	} else {
+		aggSigDB = aggsigdb.NewMemDB(deadlinerFunc("aggsigdb"))
+	}
 
 	broadcaster, err := bcast.New(ctx, eth2Cl)
 	if err != nil {

app/featureset/featureset.go

@@ -34,6 +34,8 @@ const (
 	// ConsensusParticipate enables consensus participate feature in order to participate in an ongoing consensus
 	// round while still waiting for an unsigned data from beacon node.
 	ConsensusParticipate Feature = "consensus_participate"
+
+	AggSigDBV2 Feature = "aggsigdb_v2"
 )
 
 var (
@@ -42,6 +44,7 @@ var (
 		MockAlpha:            statusAlpha,
 		EagerDoubleLinear:    statusAlpha,
 		ConsensusParticipate: statusAlpha,
+		AggSigDBV2:           statusAlpha,
 		// Add all features and there status here.
 	}