fix(ci): Windows build — env_compat shim for unsetenv in test_tone_burst_ack_payload (an old uncommitted rungCmd test edit was swept into 57aec9d without the MSVC shim)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019btwFxDt7D19SZSqPYvZnk

Author: secup

tests/test_tone_burst_ack_payload.cpp

@@ -4,6 +4,8 @@
 #include "waveform/tone_burst_ack/tone_burst_constants.hpp"
 #include "waveform/tone_burst_ack/tone_burst_payload.hpp"
 
+#include "env_compat.hpp"  // setenv/unsetenv on MSVC (knob-pinning below)
+
 #include <cassert>
 #include <cstdlib>
 #include <cstdint>