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/hashed_id8.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "sha.hpp"
+#include <boost/optional/optional.hpp>
+#include <array>
+#include <cstdint>
+#include <string>
+
+// forward declarations
+typedef struct OCTET_STRING OCTET_STRING_t;
+typedef OCTET_STRING_t Vanetza_Security_HashedId8_t;
+
+namespace vanetza
+{
+namespace pki
+{
+
+struct HashedId8
+{
+    HashedId8() = default;
+    explicit HashedId8(const Sha256Hash&);
+    explicit HashedId8(const Sha384Hash&);
+    static boost::optional<HashedId8> from_hexstring(const std::string&);
+    static boost::optional<HashedId8> from_buffer(const OCTET_STRING_t&);
+
+    std::array<std::uint8_t, 8> octets;
+};
+
+bool operator==(const HashedId8&, const HashedId8&);
+bool operator!=(const HashedId8&, const HashedId8&);
+bool operator<(const HashedId8&, const HashedId8&);
+
+std::string hexstring(const HashedId8&);
+bool valid_hashed_id8(const std::string& hex);
+
+bool lexical_cast(const std::string&, HashedId8&);
+
+bool equals(const Vanetza_Security_HashedId8_t&, const HashedId8&);
+
+} // namespace pki
+} // namespace vanetza