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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,27 @@
+#include <gtest/gtest.h>
+#include <vanetza/common/byte_sequence.hpp>
+#include <vanetza/security/public_key.hpp>
+#include <vanetza/security/v2/signature.hpp>
+#include <vanetza/security/v2/tests/check_signature.hpp>
+#include <vanetza/security/tests/serialization.hpp>
+
+using namespace vanetza::security;
+
+TEST(Signature, serialize)
+{
+    v2::Signature signature = create_random_ecdsa_signature(42);
+    check(signature, v2::serialize_roundtrip(signature));
+}
+
+TEST(Signature, WebValidator_Size)
+{
+    v2::Signature sig;
+    EcdsaSignature eSig;
+    X_Coordinate_Only x;
+    x.x = buffer_from_hexstring("8DA1F3F9F35E04C3DE77D7438988A8D57EBE44DAA021A4269E297C177C9CFE45");
+    eSig.R = x;
+    eSig.s = buffer_from_hexstring("8E128EC290785D6631961625020943B6D87DAA54919A98F7865709929A7C6E48");
+    sig = eSig;
+
+    EXPECT_EQ(66, get_size(sig));
+}