style: using effective go and refactoring

subscription.go

@@ -117,7 +117,7 @@ func (sub *Subscription) Close() {
 
 // Sub sets sub.Filters and then calls sub.Fire(ctx).
 // The subscription will be closed if the context expires.
-func (sub *Subscription) Sub(ctx context.Context, filters Filters) {
+func (sub *Subscription) Sub(_ context.Context, filters Filters) {
 	sub.Filters = filters
 	sub.Fire()
 }