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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,40 @@
+#ifndef CHANNEL_LOAD_HPP_D1JOCNLP
+#define CHANNEL_LOAD_HPP_D1JOCNLP
+
+#include <vanetza/common/unit_interval.hpp>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+class ChannelLoad : public UnitInterval
+{
+public:
+    using UnitInterval::UnitInterval;
+    ChannelLoad() = default;
+    ChannelLoad(const UnitInterval&);
+
+    /**
+     * Create ChannelLoad from rational probes
+     * \see ChannelLoad::create_from_probes
+     *
+     * \param probes_busy number of probes above busy threshold
+     * \param probes_total total number of probes
+     */
+    ChannelLoad(unsigned probes_busy, unsigned probes_total);
+
+    /**
+     * Calculate UnitInterval representing ChannelLoad from rational probes
+     * \param probes_busy number of probes above busy threshold
+     * \param probes_total total number of probes
+     * \return interval representing channel load (capped if probes_total < probes_busy)
+     */
+    static UnitInterval create_from_probes(unsigned probes_busy, unsigned probes_total);
+};
+
+} // namespace dcc
+} // namespace vanetza
+
+#endif /* CHANNEL_LOAD_HPP_D1JOCNLP */
+