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FLASHING.md says how to take a newer version of the colleague's tree (copy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/burst_budget.hpp

@@ -0,0 +1,73 @@
+#ifndef BURST_BUDGET_HPP_U5GXDCZN
+#define BURST_BUDGET_HPP_U5GXDCZN
+
+#include <vanetza/common/clock.hpp>
+#include <boost/circular_buffer.hpp>
+#include <chrono>
+#include <cstddef>
+
+namespace vanetza
+{
+
+// forward declaration
+class Runtime;
+
+namespace dcc
+{
+
+/**
+ * BurstBudget: TRC restrictions for DP0 message bursts as per C2C-CC BSP.
+ */
+class BurstBudget
+{
+public:
+    BurstBudget(const Runtime&);
+    ~BurstBudget();
+
+    /**
+     * Get current delay to remain in budget
+     * \return shortest delay not exceeding budget
+     */
+    Clock::duration delay();
+
+    /**
+     * Notify budget of consumption
+     */
+    void notify();
+
+    /**
+     * Set upper limit of messages per burst
+     * \param n burst limit
+     */
+    void burst_messages(std::size_t n);
+
+    /**
+     * Set maximum duration per burst
+     * \param d burst duration
+     */
+    void burst_duration(Clock::duration d);
+
+    /**
+     * Set minimum duration between bursts
+     * \param p burst period
+     */
+    void burst_period(Clock::duration p);
+
+    /**
+     * Get burst interval
+     * \return bust interval
+     */
+    Clock::duration burst_period() const { return m_burst_period; }
+
+private:
+    const Runtime& m_runtime;
+    boost::circular_buffer<Clock::time_point> m_messages;
+    Clock::duration m_burst_duration;
+    Clock::duration m_burst_period;
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* BURST_BUDGET_HPP_U5GXDCZN */
+