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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,39 @@
+#include <vanetza/geodesy/geodesy.hpp>
+#ifdef VANETZA_WITH_GEOGRAPHICLIB
+#   include <vanetza/geodesy/geographiclib.hpp>
+#else
+#   include <vanetza/geodesy/haversine.hpp>
+#endif
+
+namespace vanetza
+{
+namespace geodesy
+{
+
+CartesianPosition operator-(const CartesianPosition& a, const CartesianPosition& b)
+{
+    return CartesianPosition { a.x - b.x, a.y - b.y };
+}
+
+units::Length distance(const GeodeticPosition& a, const GeodeticPosition& b)
+{
+#ifdef VANETZA_WITH_GEOGRAPHICLIB
+    return geographiclib::distance(a, b);
+#else
+    return haversine::distance(a, b);
+#endif
+}
+
+CartesianPosition local_cartesian(
+        const GeodeticPosition& origin,
+        const GeodeticPosition& position)
+{
+#ifdef VANETZA_WITH_GEOGRAPHICLIB
+    return geographiclib::local_cartesian(origin, position);
+#else
+    return haversine::local_cartesian(origin, position);
+#endif
+}
+
+} // namespace geodesy
+} // namespace vanetza