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FLASHING.md says how to take a newer version of the colleague's tree (copy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_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 */
+