fix(test): add missing Arduino.h include in ported companion NodePrefs test

Upstream's version transitively pulls Stream in via NodePrefs.h ->
ConfigSerializer.h -> Arduino.h. Our fork's companion NodePrefs.h is a
plain, manually-serialized struct (no ConfigSerializer), so that chain
doesn't exist here and Stream was undeclared. Include it directly,
matching every other file in this codebase that needs Stream.

The test body itself stays #if 0 (upstream: "cannot be set yet"), so
this only fixes the build, not test coverage.

test/test_companion_node_prefs/test_companion_node_prefs.cpp

@@ -4,6 +4,8 @@
 #include <cstring>
 #include <string>
 
+#include <Arduino.h>
+
 #include "../../examples/companion_radio/NodePrefs.h"
 
 class ReplayStream : public Stream {