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/limeric_transmit_rate_control.hpp

@@ -0,0 +1,43 @@
+#ifndef LIMERIC_TRANSMIT_RATE_CONTROL_HPP_RY1TIBMJ
+#define LIMERIC_TRANSMIT_RATE_CONTROL_HPP_RY1TIBMJ
+
+#include <vanetza/dcc/limeric.hpp>
+#include <vanetza/dcc/limeric_budget.hpp>
+#include <vanetza/dcc/transmit_rate_control.hpp>
+
+namespace vanetza
+{
+
+// forward declaration
+class Runtime;
+
+namespace dcc
+{
+
+/**
+ * Transmit Rate Control implementation based on Limeric algorithm
+ */
+class LimericTransmitRateControl : public TransmitRateControl
+{
+public:
+    LimericTransmitRateControl(const Runtime&, const Limeric&);
+
+    Clock::duration delay(const Transmission&) override;
+    Clock::duration interval(const Transmission&) override;
+    void notify(const Transmission&) override;
+
+    /**
+     * Update TRC limits.
+     * Call this method whenever Limeric updates its duty cycle.
+     */
+    void update();
+
+private:
+    LimericBudget m_budget;
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* LIMERIC_TRANSMIT_RATE_CONTROL_HPP_RY1TIBMJ */
+