sfu: skip pacer allocation assertion under the race detector (#4874)

sync.Pool drops a quarter of returned items when built with -race, so the
pooled send path averages about one allocation per packet in CI and the
zero-allocation assertion flips between passing and failing. Keep the
extension checks and skip only the allocation count under race.

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

pkg/sfu/pacer/base_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/livekit/protocol/logger"
 
 	"github.com/livekit/livekit-server/pkg/sfu/bwe"
+	"github.com/livekit/livekit-server/pkg/sfu/utils"
 )
 
 // bwe.NullBWE is meant to be embedded and lacks Type
@@ -80,5 +81,7 @@ func TestSendPacketHeaderExtensionsNoAlloc(t *testing.T) {
 	require.Equal(t, 1002, w.writes)
 	require.Equal(t, 3*w.writes, w.absSendTimeLen)
 	require.Equal(t, 2*w.writes, w.transportWideLen)
-	require.Equal(t, 0.0, allocs, "allocations per SendPacket")
+	if !utils.RaceEnabled {
+		require.Equal(t, 0.0, allocs, "allocations per SendPacket")
+	}
 }

pkg/sfu/utils/norace.go

@@ -0,0 +1,6 @@
+//go:build !race
+
+package utils
+
+// RaceEnabled reports whether the binary was built with the race detector.
+const RaceEnabled = false

pkg/sfu/utils/race.go

@@ -0,0 +1,8 @@
+//go:build race
+
+package utils
+
+// RaceEnabled reports whether the binary was built with the race detector.
+// sync.Pool drops a quarter of returned items under it, so allocation counts
+// on pooled paths are not meaningful.
+const RaceEnabled = true