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/encap_service.cpp

@@ -0,0 +1,50 @@
+#include <vanetza/security/encap_service.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+EncapConfirm EncapConfirm::from(SignConfirm&& sign_confirm)
+{
+    if (sign_confirm.secured_message) {
+        return EncapConfirm { std::move(*sign_confirm.secured_message) };
+    } else {
+        return EncapConfirm { sign_confirm.error };
+    }
+}
+
+const SecuredMessage* EncapConfirm::secured_message() const
+{
+    return boost::get<SecuredMessage>(this);
+}
+
+SecuredMessage* EncapConfirm::secured_message()
+{
+    return boost::get<SecuredMessage>(this);
+}
+
+EncapConfirm dispatch(EncapRequest&& encap_request, SignService* sign_service)
+{
+    struct Dispatcher : boost::static_visitor<EncapConfirm>
+    {
+        Dispatcher(SignService* sign_service) : m_sign_service(sign_service) {}
+
+        EncapConfirm operator()(SignRequest& request)
+        {
+            if (m_sign_service) {
+                return EncapConfirm::from(m_sign_service->sign(std::move(request)));
+            } else {
+                return EncapConfirm::from(SignConfirm::failure(SignConfirmError::No_Service));
+            }
+        }
+
+        SignService* m_sign_service;
+    };
+
+    Dispatcher dispatcher(sign_service);
+    return boost::apply_visitor(dispatcher, encap_request);
+}
+
+} // namespace security
+} // namespace vanetza