refactor: move media channel handling to common/ and setup duplex channel

a duplex media channel should be more realistic, you generally both send and receive media when doing video call and
stuff

common/media/channel_test.go

@@ -0,0 +1,20 @@
+package media
+
+import (
+	"testing"
+)
+
+func TestMediaChannelStop(t *testing.T) {
+	mc := NewMediaChannel()
+
+	// This should not panic
+	mc.Stop()
+
+	// Verify that the stop channel is closed
+	select {
+	case <-mc.stopCh:
+		// Channel is closed, which is expected
+	default:
+		t.Fatal("MediaChannel stopCh should be closed after Stop()")
+	}
+}