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/dcc/interface.hpp

@@ -0,0 +1,41 @@
+#ifndef INTERFACE_HPP_4SUUTA6X
+#define INTERFACE_HPP_4SUUTA6X
+
+#include <memory>
+
+namespace vanetza
+{
+
+// forward declarations
+class ChunkPacket;
+
+namespace dcc
+{
+
+// forward declarations
+struct DataRequest;
+
+/**
+ * DCC_access interface for data request from upper layers
+ */
+class RequestInterface
+{
+public:
+    virtual void request(const DataRequest&, std::unique_ptr<ChunkPacket>) = 0;
+    virtual ~RequestInterface() = default;
+};
+
+/**
+ * Null implemenation of DCC data request interface
+ */
+class NullRequestInterface : public RequestInterface
+{
+public:
+    void request(const DataRequest&, std::unique_ptr<ChunkPacket>) override {}
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* INTERFACE_HPP_4SUUTA6X */
+