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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,63 @@
+#ifndef LIFETIME_HPP_XYTSNW3J
+#define LIFETIME_HPP_XYTSNW3J
+
+#include <vanetza/common/bit_number.hpp>
+#include <vanetza/geonet/serialization.hpp>
+#include <vanetza/units/time.hpp>
+#include <boost/operators.hpp>
+#include <cstdint>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+class Lifetime : public boost::totally_ordered<Lifetime>
+{
+public:
+    static constexpr uint8_t multiplier_mask = 0xFC;
+    static constexpr uint8_t base_mask = 0x03;
+
+    enum class Base {
+        Fifty_Milliseconds = 0,
+        One_Second = 1,
+        Ten_Seconds = 2,
+        Hundred_Seconds = 3
+    };
+
+    static const Lifetime zero();
+
+    Lifetime();
+    Lifetime(Base base, BitNumber<uint8_t, 6> multiplier);
+    void set(Base base, BitNumber<uint8_t, 6> multiplier);
+    uint8_t raw() const { return m_lifetime; }
+    void raw(uint8_t raw) { m_lifetime = raw; }
+
+    bool operator<(const Lifetime&) const;
+    bool operator==(const Lifetime&) const;
+
+    /**
+     * Decodes stored lifetime
+     * \return lifetime as duration quantity
+     */
+    units::Duration decode() const;
+
+    /**
+     * Encode duration in lifetime object
+     * \note Precision loss might occur
+     * \param duration Lifetime duration
+     */
+    void encode(units::Duration);
+
+private:
+    uint8_t m_lifetime;
+};
+
+void serialize(const Lifetime&, OutputArchive&);
+void deserialize(Lifetime&, InputArchive&);
+
+} // namespace geonet
+} // namespace vanetza
+
+#endif /* LIFETIME_HPP_XYTSNW3J */
+