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/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