Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/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);
+}