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FLASHING.md says how to take a newer version of the colleague's tree (copy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/security/v2/tests/payload.cpp

@@ -0,0 +1,38 @@
+#include <gtest/gtest.h>
+#include <vanetza/security/v2/payload.hpp>
+#include <vanetza/security/v2/tests/check_payload.hpp>
+#include <vanetza/security/tests/serialization.hpp>
+
+using namespace vanetza;
+using namespace vanetza::security::v2;
+
+TEST(Payload, serialize_cohesive)
+{
+    Payload p;
+    p.type = PayloadType::Unsecured;
+    p.data = CohesivePacket({ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 }, OsiLayer::Application);
+
+    check(p, serialize_roundtrip(p));
+}
+
+TEST(Payload, serialize_chunk)
+{
+    Payload p;
+    p.type = PayloadType::Encrypted;
+    ChunkPacket packet;
+    packet[OsiLayer::Network] = ByteBuffer { 1, 2, 3, 4 };
+    packet[OsiLayer::Transport] = ByteBuffer { 5, 6, 7, 8 };
+    packet[OsiLayer::Application] = ByteBuffer { 9, 10, 11, 12 };
+    p.data = packet;
+
+    check(p, serialize_roundtrip(p));
+}
+
+TEST(Payload, size)
+{
+    Payload p;
+    p.type = PayloadType::Signed;
+    p.data = CohesivePacket({ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, OsiLayer::Session);
+    EXPECT_EQ(1 /* type */ + 1 /* length coding */ + 10 /* bytes */, get_size(p));
+}
+