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/geonet/tests/basic_header.cpp

@@ -0,0 +1,43 @@
+#include <gtest/gtest.h>
+#include <vanetza/geonet/basic_header.hpp>
+#include <vanetza/geonet/data_request.hpp>
+#include <vanetza/geonet/tests/serialization.hpp>
+
+using namespace vanetza::geonet;
+using vanetza::units::si::seconds;
+
+TEST(BasicHeader, ctor) {
+    MIB mib;
+    BasicHeader a(mib);
+    EXPECT_EQ(a.lifetime, mib.itsGnDefaultPacketLifetime);
+    EXPECT_EQ(a.hop_limit, mib.itsGnDefaultHopLimit);
+
+    DataRequest req(mib);
+    req.maximum_lifetime.encode(31.0 * seconds);
+    req.max_hop_limit = 4;
+    BasicHeader b(req, mib);
+    EXPECT_EQ(b.lifetime.decode(), 31.0 * seconds);
+    EXPECT_EQ(b.hop_limit, 4);
+
+    ShbDataRequest shb(mib);
+    BasicHeader c(shb, mib);
+    EXPECT_EQ(c.hop_limit, 1);
+}
+
+TEST(BasicHeader, serialization) {
+    BasicHeader a;
+    a.version = 2;
+    a.next_header = NextHeaderBasic::Secured;
+    a.reserved = 0xC3;
+    a.lifetime.raw(0x89);
+    a.hop_limit = 218;
+
+    BasicHeader b = serialize_roundtrip(a);
+    EXPECT_EQ(a.version, b.version);
+    EXPECT_EQ(a.next_header, b.next_header);
+    EXPECT_EQ(a.reserved, b.reserved);
+    EXPECT_EQ(a.lifetime, b.lifetime);
+    EXPECT_EQ(a.hop_limit, b.hop_limit);
+
+    EXPECT_EQ(BasicHeader::length_bytes, serialize_length(a));
+}