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/gbc_header.cpp

@@ -0,0 +1,42 @@
+#include "gbc_header.hpp"
+#include "areas.hpp"
+#include <stdexcept>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+Area GeoBroadcastHeader::destination(HeaderType ht) const
+{
+    decltype(Area::shape) shape;
+    switch (ht) {
+        case HeaderType::GeoBroadcast_Circle:
+            shape = Circle();
+            break;
+        case HeaderType::GeoBroadcast_Rect:
+            shape = Rectangle();
+            break;
+        case HeaderType::GeoBroadcast_Elip:
+            shape = Ellipse();
+            break;
+        default:
+            throw std::runtime_error("Invalid GBC header type");
+            break;
+    }
+
+    return detail::GbcGacHeader::destination(shape);
+}
+
+void serialize(const GeoBroadcastHeader& header, OutputArchive& ar)
+{
+    detail::serialize(header, ar);
+}
+
+void deserialize(GeoBroadcastHeader& header, InputArchive& ar)
+{
+    detail::deserialize(header, ar);
+}
+
+} // namespace geonet
+} // namespace vanetza