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/state_machine.hpp

@@ -0,0 +1,37 @@
+#ifndef STATE_MACHINE_HPP_0MHYOQU7
+#define STATE_MACHINE_HPP_0MHYOQU7
+
+#include <vanetza/dcc/channel_load.hpp>
+#include <vanetza/common/clock.hpp>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+/**
+ * State machine interface used for Transmit Rate Control
+ */
+class StateMachine
+{
+public:
+    /**
+     * Trigger state transition by updated channel load
+     * \param cl new channel load measurement
+     */
+    virtual void update(ChannelLoad cl) = 0;
+
+    /**
+     * Get current transmission interval
+     * \return duration between two transmissions
+     */
+    virtual Clock::duration transmission_interval() const = 0;
+
+    virtual ~StateMachine() = default;
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* STATE_MACHINE_HPP_0MHYOQU7 */
+