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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,34 @@
+#include <vanetza/common/its_aid.hpp>
+#include <vanetza/security/delegating_security_entity.hpp>
+#include <stdexcept>
+
+namespace vanetza
+{
+namespace security
+{
+
+DelegatingSecurityEntity::DelegatingSecurityEntity(std::unique_ptr<SignService> sign, std::unique_ptr<VerifyService> verify) :
+    m_sign_service(std::move(sign)),
+    m_verify_service(std::move(verify))
+{
+    if (!m_sign_service) {
+        throw std::invalid_argument("SN-SIGN service is not callable");
+    } else if (!m_verify_service) {
+        throw std::invalid_argument("SN-VERIFY service is not callable");
+    }
+}
+
+EncapConfirm DelegatingSecurityEntity::encapsulate_packet(EncapRequest&& encap_request)
+{
+    return dispatch(std::move(encap_request), m_sign_service.get());
+}
+
+DecapConfirm DelegatingSecurityEntity::decapsulate_packet(DecapRequest&& decap_request)
+{
+    SecuredMessageView msg_view { decap_request.sec_packet };
+    auto verify_confirm = m_verify_service->verify(VerifyRequest { msg_view });
+    return DecapConfirm::from(std::move(verify_confirm), msg_view);
+}
+
+} // namespace security
+} // namespace vanetza