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.hpp

@@ -0,0 +1,30 @@
+#ifndef CHECK_SIGNATURE_HPP_7RESWTUO
+#define CHECK_SIGNATURE_HPP_7RESWTUO
+
+#include <vanetza/security/v2/signature.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+void check(const EcdsaSignature&, const EcdsaSignature&);
+void check(const EcdsaSignatureFuture&, const EcdsaSignatureFuture&);
+
+/**
+ * \brief create a random EcdsaSignature
+ * \param seed the optional seed for the RNG
+ * \return created signature
+ */
+EcdsaSignature create_random_ecdsa_signature(int seed = 0);
+
+namespace v2
+{
+
+void check(const Signature&, const Signature&);
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* CHECK_SIGNATURE_HPP_7RESWTUO */