Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/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 */
+