Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/security/v2/tests/check_payload.hpp

@@ -0,0 +1,34 @@
+#ifndef CHECK_PAYLOAD_HPP_YNRGOKGC
+#define CHECK_PAYLOAD_HPP_YNRGOKGC
+
+#include <gtest/gtest.h>
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/common/serialization_buffer.hpp>
+#include <vanetza/security/v2/payload.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+inline void check(const PacketVariant& expected, const PacketVariant& actual)
+{
+    ByteBuffer expected_buf, actual_buf;
+    serialize_into_buffer(expected, expected_buf);
+    serialize_into_buffer(actual, actual_buf);
+    EXPECT_EQ(expected_buf, actual_buf);
+}
+
+inline void check(const Payload& expected, const Payload& actual)
+{
+    EXPECT_EQ(expected.type, actual.type);
+    check(expected.data, actual.data);
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* CHECK_PAYLOAD_HPP_YNRGOKGC */