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/asn1/packet_visitor.hpp

@@ -0,0 +1,90 @@
+#ifndef PACKET_VISITOR_HPP_UYSI8HXZ
+#define PACKET_VISITOR_HPP_UYSI8HXZ
+
+#include <vanetza/asn1/asn1c_conversion.hpp>
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/net/chunk_packet.hpp>
+#include <vanetza/net/cohesive_packet.hpp>
+#include <vanetza/net/osi_layer.hpp>
+#include <vanetza/net/packet_variant.hpp>
+#include <boost/variant/static_visitor.hpp>
+#include <memory>
+
+namespace vanetza
+{
+namespace asn1
+{
+
+/**
+ * PacketVisitor is a helper to extract the ASN.1 wrapper object from a packet's application layer.
+ * This is a generalised version of the implementation found in Artery before.
+ *
+ * ChunkPacket's application layer is simply casted for the sake of speed whenever possible.
+ * When casting fails, this helper can fall back to deserialization, see allow_chunk_deserialization.
+ * Deserialization is the only option for CohesivePacket's application layer.
+ *
+ * \param T is the asn1c_wrapper<> type, e.g. Cam or Denm
+ */
+template<typename T>
+class PacketVisitor : public boost::static_visitor<std::shared_ptr<const T>>
+{
+    public:
+        std::shared_ptr<const T> operator()(const ChunkPacket& packet)
+        {
+            using byte_buffer_impl = convertible::byte_buffer_impl<T>;
+            auto impl = dynamic_cast<const byte_buffer_impl*>(packet[OsiLayer::Application].ptr());
+            if (impl) {
+                m_wrapper = impl->wrapper();
+            } else if (m_deserialize_chunk) {
+                deserialize(create_byte_view(packet, m_start_layer, OsiLayer::Application));
+            } else {
+                m_wrapper.reset();
+            }
+            return m_wrapper;
+        }
+
+        std::shared_ptr<const T> operator()(const CohesivePacket& packet)
+        {
+            deserialize(create_byte_view(packet, m_start_layer, OsiLayer::Application));
+            return m_wrapper;
+        }
+
+        std::shared_ptr<const T> get_shared_wrapper() const { return m_wrapper; }
+
+        /**
+         * Allow deserialization attempt of ChunkPacket when casting failed.
+         * \param flag true allows deserialization
+         */
+        void allow_chunk_deserialization(bool flag)
+        {
+            m_deserialize_chunk = flag;
+        }
+
+        /**
+         * Set OSI layer where deserialization shall start, it always stops at end of OsiLayer::Application.
+         * By default, PacketVisitors starts at OsiLayer::Session for compatibility with BTP parser functions.
+         * \param start OSI layer
+         */
+        void start_deserialization_at(OsiLayer start)
+        {
+            m_start_layer = start;
+        }
+
+    private:
+        void deserialize(const byte_view_range& range)
+        {
+            auto tmp = std::make_shared<T>();
+            bool decoded = tmp->decode(range.begin().raw(), range.size());
+            m_wrapper = decoded ? tmp : nullptr;
+        }
+
+        std::shared_ptr<const T> m_wrapper;
+        bool m_deserialize_chunk = true;
+        OsiLayer m_start_layer = OsiLayer::Session;
+};
+
+} // namespace asn1
+} // namespace vanetza
+
+#endif /* PACKET_VISITOR_HPP_UYSI8HXZ */
+