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.cpp

@@ -0,0 +1,20 @@
+#include "signed_data.hpp"
+#include <vanetza/asn1/security/Ieee1609Dot2Content.h>
+
+namespace vanetza
+{
+namespace pki
+{
+
+void SignedData::move_into(Vanetza_Security_Ieee1609Dot2Data_t& dest) &&
+{
+    auto* self = content();
+    // Release anything dest already held (normally none) to avoid leaks.
+    ASN_STRUCT_FREE(asn_DEF_Vanetza_Security_Ieee1609Dot2Content, dest.content);
+    dest.protocolVersion = self->protocolVersion;
+    dest.content = self->content;
+    self->content = nullptr;
+}
+
+} // namespace pki
+} // namespace vanetza