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/encryption_parameter.cpp

@@ -0,0 +1,17 @@
+#include <gtest/gtest.h>
+#include <vanetza/common/byte_sequence.hpp>
+#include <vanetza/security/v2/encryption_parameter.hpp>
+#include <vanetza/security/v2/tests/check_encryption_parameter.hpp>
+#include <vanetza/security/tests/serialization.hpp>
+#include <algorithm>
+
+using namespace vanetza::security::v2;
+
+TEST(EncryptionParameter, Nonce)
+{
+    Nonce nonce;
+    auto random = vanetza::random_byte_sequence(nonce.size());
+    std::copy_n(random.begin(), nonce.size(), nonce.begin());
+    EncryptionParameter param = nonce;
+    check(param, serialize_roundtrip(param));
+}