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/common/byte_buffer_convertible.cpp

@@ -0,0 +1,53 @@
+#include "byte_buffer_convertible.hpp"
+#include <algorithm>
+#include <iterator>
+
+namespace vanetza
+{
+namespace convertible
+{
+
+std::unique_ptr<byte_buffer> byte_buffer::duplicate() const
+{
+    ByteBuffer duplicate;
+    this->convert(duplicate);
+    std::unique_ptr<byte_buffer> result {
+        new byte_buffer_impl<ByteBuffer>(std::move(duplicate))
+    };
+    return result;
+}
+
+byte_buffer_impl<std::string>::byte_buffer_impl(const std::string& str) : m_buffer(str) {}
+byte_buffer_impl<std::string>::byte_buffer_impl(std::string&& str) : m_buffer(std::move(str)) {}
+
+void byte_buffer_impl<std::string>::convert(ByteBuffer& buffer) const
+{
+    buffer.clear();
+    std::copy(m_buffer.begin(), m_buffer.end(), std::back_inserter(buffer));
+}
+
+std::size_t byte_buffer_impl<std::string>::size() const
+{
+    return m_buffer.size();
+}
+
+std::unique_ptr<byte_buffer> byte_buffer_impl<std::nullptr_t>::duplicate() const
+{
+    return std::unique_ptr<byte_buffer> { new byte_buffer_impl<std::nullptr_t>() };
+}
+
+} // namespace convertible
+
+ByteBufferConvertible::ByteBufferConvertible(const ByteBufferConvertible& other) :
+    m_wrapper(other.m_wrapper->duplicate())
+{
+}
+
+ByteBufferConvertible& ByteBufferConvertible::operator=(const ByteBufferConvertible& other)
+{
+    m_wrapper = other.m_wrapper->duplicate();
+    return *this;
+}
+
+} // namespace vanetza
+