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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,20 @@
+#include <vanetza/facilities/path_point.hpp>
+#include <gtest/gtest.h>
+
+namespace units = vanetza::units;
+using vanetza::facilities::PathPoint;
+
+TEST(PathPoint, chord_length) {
+    PathPoint a;
+    a.longitude = 12.14094444 * units::degrees;
+    a.latitude = 49.53858333 * units::degrees;
+
+    PathPoint b;
+    b.longitude = 12.27191666 * units::degrees;
+    b.latitude = 49.72394444 * units::degrees;
+
+    EXPECT_EQ(chord_length(a, b), chord_length(b, a));
+
+    units::Length length = chord_length(a, b);
+    EXPECT_NEAR(22692.54, length / units::si::meters, 0.01);
+}