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/delegating_security_entity.hpp

@@ -0,0 +1,42 @@
+#ifndef DELEGATING_SECURITY_ENTITY_HPP_W1MFSVEN
+#define DELEGATING_SECURITY_ENTITY_HPP_W1MFSVEN
+
+#include <vanetza/security/security_entity.hpp>
+#include <vanetza/security/sign_service.hpp>
+#include <vanetza/security/verify_service.hpp>
+#include <memory>
+
+namespace vanetza
+{
+namespace security
+{
+
+/**
+ * Implementation of SecurityEntity delegating to SignService and VerifyService
+ */
+class DelegatingSecurityEntity : public SecurityEntity
+{
+public:
+    /**
+     * \brief Create security entity from primitive services.
+     *
+     * A std::invalid_argument exception is thrown at construction
+     * if any given service is not callable.
+     *
+     * \param sign SN-SIGN service
+     * \param verify SN-VERIFY service
+     */
+    DelegatingSecurityEntity(std::unique_ptr<SignService> sign, std::unique_ptr<VerifyService> verify);
+
+    EncapConfirm encapsulate_packet(EncapRequest&& encap_request) override;
+    DecapConfirm decapsulate_packet(DecapRequest&& decap_request) override;
+
+private:
+    std::unique_ptr<SignService> m_sign_service;
+    std::unique_ptr<VerifyService> m_verify_service;
+};
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* DELEGATING_SECURITY_ENTITY_HPP_W1MFSVEN */