chore: improve testing and increase coverage (#794)

This diff improves testing and increases coverage inside the
./internal/netxlite and ./internal/tracex packages.

See https://github.com/ooni/probe/issues/2121

internal/tracex/event_test.go

@@ -0,0 +1,36 @@
+package tracex
+
+import "testing"
+
+func TestUnusedEventsNames(t *testing.T) {
+	// Tests that we don't break the names of events we're currently
+	// not getting the name of directly even if they're saved.
+
+	t.Run("EventQUICHandshakeStart", func(t *testing.T) {
+		ev := &EventQUICHandshakeStart{}
+		if ev.Name() != "quic_handshake_start" {
+			t.Fatal("invalid event name")
+		}
+	})
+
+	t.Run("EventQUICHandshakeDone", func(t *testing.T) {
+		ev := &EventQUICHandshakeDone{}
+		if ev.Name() != "quic_handshake_done" {
+			t.Fatal("invalid event name")
+		}
+	})
+
+	t.Run("EventTLSHandshakeStart", func(t *testing.T) {
+		ev := &EventTLSHandshakeStart{}
+		if ev.Name() != "tls_handshake_start" {
+			t.Fatal("invalid event name")
+		}
+	})
+
+	t.Run("EventTLSHandshakeDone", func(t *testing.T) {
+		ev := &EventTLSHandshakeDone{}
+		if ev.Name() != "tls_handshake_done" {
+			t.Fatal("invalid event name")
+		}
+	})
+}