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/transmission.hpp

@@ -0,0 +1,41 @@
+#ifndef TRANSMISSION_HPP_SDC4RMQE
+#define TRANSMISSION_HPP_SDC4RMQE
+
+#include <vanetza/access/data_rates.hpp>
+#include <vanetza/common/clock.hpp>
+#include <vanetza/dcc/profile.hpp>
+#include <cstddef>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+class Transmission
+{
+public:
+    virtual Profile profile() const = 0;
+    virtual const access::DataRateG5* data_rate() const = 0;
+    virtual std::size_t body_length() const = 0;
+    virtual Clock::duration channel_occupancy() const;
+    virtual ~Transmission() = default;
+};
+
+struct TransmissionLite : public Transmission
+{
+    constexpr TransmissionLite(Profile dp, std::size_t len) : m_profile(dp), m_length(len) {}
+
+    Profile m_profile;
+    std::size_t m_length = 0; /*< length in bytes of MAC frame body */
+    const access::DataRateG5* m_data_rate = nullptr;
+
+    Profile profile() const override { return m_profile; }
+    const access::DataRateG5* data_rate() const override { return m_data_rate; }
+    std::size_t body_length() const override { return m_length; }
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* TRANSMISSION_HPP_SDC4RMQE */
+