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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,45 @@
+#include <gtest/gtest.h>
+#include <vanetza/common/byte_sequence.hpp>
+#include <vanetza/security/signature.hpp>
+#include <vanetza/security/v2/tests/check_ecc_point.hpp>
+#include <vanetza/security/v2/tests/check_signature.hpp>
+#include <vanetza/security/v2/tests/check_visitor.hpp>
+#include <boost/variant/apply_visitor.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+void check(const EcdsaSignature& expected, const EcdsaSignature& actual)
+{
+    check(expected.R, actual.R);
+    EXPECT_EQ(expected.s, actual.s);
+}
+
+void check(const EcdsaSignatureFuture& expected, const EcdsaSignatureFuture& actual)
+{
+    check(expected.get(), actual.get());
+}
+
+EcdsaSignature create_random_ecdsa_signature(int seed)
+{
+    const std::size_t field = v2::field_size(v2::PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256);
+    EcdsaSignature signature;
+    signature.s = random_byte_sequence(field, seed);
+    signature.R = X_Coordinate_Only { random_byte_sequence(field, ~seed) };
+    return signature;
+}
+
+namespace v2
+{
+
+void check(const Signature& expected, const Signature& actual)
+{
+    ASSERT_EQ(get_type(expected), get_type(actual));
+    // TODO boost::apply_visitor(check_visitor<Signature>(), expected, actual);
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza