feat(eventbus): warn applications whenever events aren't read

Adds logging for the EventBus, Mainly a periodical warning for applications whenever they
are slow in reading or do not read EventBus notifications. It came up after debugging a
very tricky case where a bugged Server side application wasn't reading `EvtConnectednessChanged`
events, which manifested in the server's inability to accept new streams as connection handling
logic deadlocked on _sync_ Notifee's  `Connected` callbacks which emit the events.

P.S. This change should save some time for future application developers.

p2p/host/eventbus/basic.go

@@ -6,10 +6,14 @@ import (
 	"reflect"
 	"sync"
 	"sync/atomic"
+	"time"
 
+	logging "github.com/ipfs/go-log/v2"
 	"github.com/libp2p/go-libp2p/core/event"
 )
 
+var log = logging.Logger("eventbus")
+
 // /////////////////////
 // BUS
 
@@ -347,7 +351,27 @@ func (n *node) emit(evt interface{}) {
 	}
 
 	for _, ch := range n.sinks {
-		ch <- evt
+		select {
+		case ch <- evt:
+		default:
+			n.emitWithWarn(evt, ch)
+		}
 	}
 	n.lk.Unlock()
 }
+
+func (n *node) emitWithWarn(evt any, sink chan any) {
+	// warn periodically, otherwise a single log may get lost
+	t := time.NewTicker(time.Millisecond * 100)
+	defer t.Stop()
+
+	for {
+		select {
+		case sink <- evt:
+			return
+		case <-t.C:
+			// warn node operator or dev about slow event consumption by application
+			log.Warn("SLOW EVENT CONSUMER OF TYPE %s", n.typ)
+		}
+	}
+}