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_budget.hpp

@@ -0,0 +1,67 @@
+#ifndef LIMERIC_BUDGET_HPP_RQYL16AG
+#define LIMERIC_BUDGET_HPP_RQYL16AG
+
+#include <vanetza/common/clock.hpp>
+
+namespace vanetza
+{
+
+// forward declaration
+class Runtime;
+
+namespace dcc
+{
+
+// forward declaration
+class DutyCyclePermit;
+
+/**
+ * LimericBudget models Annex B of TS 102 687 v1.2.1, i.e.
+ * packet handling to meet the channel occupancy limit
+ */
+class LimericBudget
+{
+public:
+    LimericBudget(const DutyCyclePermit&, const Runtime&);
+
+    /**
+     * Get delay until next transmission is allowed
+     * \return remaining transmission delay
+     */
+    Clock::duration delay();
+
+    /**
+     * Get current interval between transmissions
+     * \return transmission interval
+     */
+    Clock::duration interval();
+
+    /**
+     * Notify budget about transmission activity
+     * \param tx_on over-the-air duration of transmission
+     */
+    void notify(Clock::duration tx_on);
+
+    /**
+     * Recalculate current transmission interval.
+     *
+     * Transmission interval is derived from Limeric's current permitted duty cycle.
+     * Hence, this method should be called whenever Limeric changes its duty cycle.
+     */
+    void update();
+
+private:
+    Clock::duration clamp_interval(Clock::duration) const;
+
+    const DutyCyclePermit& m_duty_cycle_permit;
+    const Runtime& m_runtime;
+    Clock::duration m_interval;
+    Clock::time_point m_tx_start;
+    Clock::duration m_tx_on;
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* LIMERIC_BUDGET_HPP_RQYL16AG */
+