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/tools/pki/signed_data.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <vanetza/asn1/asn1c_wrapper.hpp>
+#include <vanetza/asn1/security/EtsiTs103097Data-Signed.h>
+#include <vanetza/asn1/security/Ieee1609Dot2Data.h>
+
+namespace vanetza
+{
+namespace pki
+{
+
+class SignedData : public asn1::asn1c_oer_wrapper<Vanetza_Security_EtsiTs103097Data_Signed_55P0_t>
+{
+public:
+    using wrapper = asn1::asn1c_oer_wrapper<Vanetza_Security_EtsiTs103097Data_Signed_55P0_t>;
+
+    SignedData() : wrapper(asn_DEF_Vanetza_Security_EtsiTs103097Data_Signed_55P0)
+    {
+    }
+
+    /**
+     * Graft the envelope into a parent that takes over ownership.
+     * Consuming: only callable on an rvalue, leaving the source empty.
+     *
+     * \param dest Ieee1609Dot2Data field of the parent to move the envelope into
+     */
+    void move_into(Vanetza_Security_Ieee1609Dot2Data_t& dest) &&;
+};
+
+} // namespace pki
+} // namespace vanetza