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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,56 @@
+#include <gtest/gtest.h>
+#include <vanetza/geonet/gbc_gac_header.hpp>
+#include <vanetza/geonet/tests/serialization.hpp>
+#include <vanetza/units/angle.hpp>
+
+using namespace vanetza::geonet;
+using vanetza::geonet::detail::GbcGacHeader;
+using vanetza::units::degree;
+
+TEST(GbcGacHeader, ctor) {
+    GbcGacHeader hdr;
+    EXPECT_EQ(0, static_cast<SequenceNumber::value_type>(hdr.sequence_number));
+    EXPECT_EQ(0, hdr.reserved1);
+    EXPECT_EQ(LongPositionVector(), hdr.source_position);
+    EXPECT_EQ(0, hdr.geo_area_pos_latitude.value());
+    EXPECT_EQ(0, hdr.geo_area_pos_longitude.value());
+    EXPECT_EQ(0, hdr.distance_a.value());
+    EXPECT_EQ(0, hdr.distance_b.value());
+    EXPECT_EQ(0, hdr.angle.value());
+    EXPECT_EQ(0, hdr.reserved2);
+}
+
+TEST(GbcGacHeader, position) {
+    GbcGacHeader hdr;
+    GeodeticPosition pos { 12.3456789 * degree, 123.4567891 * degree };
+    hdr.position(pos);
+    EXPECT_EQ(123456789, hdr.geo_area_pos_latitude.value());
+    EXPECT_EQ(1234567891, hdr.geo_area_pos_longitude.value());
+    EXPECT_EQ(pos.latitude, hdr.position().latitude);
+    EXPECT_EQ(pos.longitude, hdr.position().longitude);
+}
+
+TEST(GbcGacHeader, serialization) {
+    GbcGacHeader a;
+    a.sequence_number = SequenceNumber(18);
+    a.reserved1 = 0x1234;
+    a.source_position.latitude = geo_angle_i32t::from_value(0xAABB);
+    a.source_position.longitude = geo_angle_i32t::from_value(0xCCDD);
+    a.distance_a = distance_u16t::from_value(0x1234);
+    a.distance_b = distance_u16t::from_value(0x4321);
+    a.angle = angle_u16t::from_value(0x1337);
+    a.reserved2 = 0x2020;
+
+    GbcGacHeader b = serialize_roundtrip(a);
+    EXPECT_EQ(a.sequence_number, b.sequence_number);
+    EXPECT_EQ(a.reserved1, b.reserved1);
+    EXPECT_EQ(a.source_position, b.source_position);
+    EXPECT_EQ(a.geo_area_pos_latitude, b.geo_area_pos_latitude);
+    EXPECT_EQ(a.geo_area_pos_longitude, b.geo_area_pos_longitude);
+    EXPECT_EQ(a.distance_a, b.distance_a);
+    EXPECT_EQ(a.distance_b, b.distance_b);
+    EXPECT_EQ(a.angle, b.angle);
+    EXPECT_EQ(a.reserved2, b.reserved2);
+
+    EXPECT_EQ(GbcGacHeader::length_bytes, serialize_length(a));
+}