test: fix two data races in the test suites (#4878)

* test: stop registering the global DefaultConfig with the logger

InitLoggerFromConfig hands the pointer to zaputil.ComponentLeveler as its
level resolver, and protocol a879e94 gave logger.Config a
ResolveComponentLevel that takes c.lock. The two test packages passed
&config.DefaultConfig.Logging, so every first-time component level
resolution locked a mutex inside the global DefaultConfig while
config.NewConfig marshalled that same global from another goroutine:

  Read at 0x39baa08  yaml.Marshal -> pkg/config/config.go:633 (NewConfig)
  Write at 0x39baa08 ComponentLeveler.resolve -> zaputil/leveler.go:117

That tripped the race detector in pkg/rtc TestPreferMediaCodecForPublisher
and broke CI on master.

Register a test-local LoggingConfig instead, so the logger never touches
the global that NewConfig reads. DefaultConfig.Logging only ever sets
PionLevel, so behavior is unchanged. A plain struct copy is not an option
here: logger.Config holds a mutex and vet's copylocks would reject it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* test: make RTCClient callbacks safe to set while the client runs

The scenario tests assign c2.OnDataReceived after waitUntilConnected, so
the assignment raced the data channel goroutine already reading the field
in handleDataMessage:

  Read  test/client.(*RTCClient).handleDataMessage  client.go:1146
  Write test.scenarioDataPublish.func1              scenarios.go:160

This is what failed TestMultinodeDataPublishing on master.

Replace the three exported callback fields with atomic pointers behind
SetOnConnected/SetOnDataReceived/SetOnDataUnlabeledReceived. OnConnected
and OnDataUnlabeledReceived have no writers today, but they are read from
the same background goroutines and would race the moment one appeared, so
all three move together rather than leaving a split API on one struct.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

test/client/client.go

@@ -94,10 +94,12 @@ type RTCClient struct {
 	// remote tracks waiting to be processed
 	pendingRemoteTracks []*webrtc.TrackRemote
 
-	pendingTrackWriters     []TrackWriter
-	OnConnected             func()
-	OnDataReceived          func(data []byte, sid string)
-	OnDataUnlabeledReceived func(data []byte)
+	pendingTrackWriters []TrackWriter
+	// callbacks are set by tests while the client is already running, and read
+	// from the signal and data channel goroutines
+	onConnected             atomic.Pointer[func()]
+	onDataReceived          atomic.Pointer[func(data []byte, sid string)]
+	onDataUnlabeledReceived atomic.Pointer[func(data []byte)]
 	refreshToken            string
 
 	// map of livekit.ParticipantID and last packet
@@ -346,8 +348,8 @@ func (c *RTCClient) createTransport(rtcconf webrtc.Configuration) error {
 		}
 		c.pendingDataTrackWriters = nil
 
-		if c.OnConnected != nil {
-			go c.OnConnected()
+		if f := c.onConnected.Load(); f != nil {
+			go (*f)()
 		}
 	})
 	publisherHandler.OnOfferCalls(c.onOffer)
@@ -440,8 +442,8 @@ func (c *RTCClient) createTransport(rtcconf webrtc.Configuration) error {
 			}
 			c.pendingDataTrackWriters = nil
 
-			if c.OnConnected != nil {
-				go c.OnConnected()
+			if f := c.onConnected.Load(); f != nil {
+				go (*f)()
 			}
 		})
 		subscriberHandler.OnFullyEstablishedCalls(func() {
@@ -472,6 +474,21 @@ func (c *RTCClient) ID() livekit.ParticipantID {
 	return c.id
 }
 
+// SetOnConnected is safe to call after the client is running.
+func (c *RTCClient) SetOnConnected(f func()) {
+	c.onConnected.Store(&f)
+}
+
+// SetOnDataReceived is safe to call after the client is running.
+func (c *RTCClient) SetOnDataReceived(f func(data []byte, sid string)) {
+	c.onDataReceived.Store(&f)
+}
+
+// SetOnDataUnlabeledReceived is safe to call after the client is running.
+func (c *RTCClient) SetOnDataUnlabeledReceived(f func(data []byte)) {
+	c.onDataUnlabeledReceived.Store(&f)
+}
+
 // create an offer for the server
 func (c *RTCClient) Run() error {
 	c.conn.SetCloseHandler(func(code int, text string) error {
@@ -1143,15 +1160,15 @@ func (c *RTCClient) handleDataMessage(kind livekit.DataPacket_Kind, data []byte)
 	}
 	dp.Kind = kind
 	if val, ok := dp.Value.(*livekit.DataPacket_User); ok {
-		if c.OnDataReceived != nil {
-			c.OnDataReceived(val.User.Payload, val.User.ParticipantSid)
+		if f := c.onDataReceived.Load(); f != nil {
+			(*f)(val.User.Payload, val.User.ParticipantSid)
 		}
 	}
 }
 
 func (c *RTCClient) handleDataMessageUnlabeled(data []byte) {
-	if c.OnDataUnlabeledReceived != nil {
-		c.OnDataUnlabeledReceived(data)
+	if f := c.onDataUnlabeledReceived.Load(); f != nil {
+		(*f)(data)
 	}
 }