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.hpp

@@ -0,0 +1,109 @@
+#ifndef BYTE_BUFFER_CONVERTIBLE_HPP_CFOQNR35
+#define BYTE_BUFFER_CONVERTIBLE_HPP_CFOQNR35
+
+#include <vanetza/common/byte_buffer.hpp>
+#include <cstddef>
+#include <memory>
+#include <string>
+#include <type_traits>
+
+namespace vanetza
+{
+namespace convertible
+{
+
+struct byte_buffer
+{
+    virtual void convert(ByteBuffer&) const = 0;
+    virtual std::size_t size() const = 0;
+    virtual std::unique_ptr<byte_buffer> duplicate() const;
+    virtual ~byte_buffer() {}
+};
+
+template<class T>
+struct byte_buffer_impl;
+
+template<>
+struct byte_buffer_impl<ByteBuffer> : public byte_buffer
+{
+    byte_buffer_impl(ByteBuffer&& buffer) : m_buffer(std::move(buffer)) {}
+    void convert(ByteBuffer& buf) const override { buf = m_buffer; }
+    std::size_t size() const override { return m_buffer.size(); }
+
+    ByteBuffer m_buffer;
+};
+
+template<>
+struct byte_buffer_impl<std::unique_ptr<ByteBuffer>> : public byte_buffer
+{
+    byte_buffer_impl(std::unique_ptr<ByteBuffer> buf) :
+        m_buffer(std::move(buf)) {}
+    void convert(ByteBuffer& buf) const override { buf = *m_buffer; }
+    std::size_t size() const override { return m_buffer->size(); }
+
+    std::unique_ptr<ByteBuffer> m_buffer;
+};
+
+template<>
+struct byte_buffer_impl<std::string> : public byte_buffer
+{
+    byte_buffer_impl(const std::string& str);
+    byte_buffer_impl(std::string&& str);
+    void convert(ByteBuffer& buffer) const override;
+    std::size_t size() const override;
+
+    std::string m_buffer;
+};
+
+template<>
+struct byte_buffer_impl<std::nullptr_t> : public byte_buffer
+{
+    void convert(ByteBuffer& buffer) const override { buffer.clear(); }
+    std::size_t size() const override { return 0; }
+    std::unique_ptr<byte_buffer> duplicate() const override;
+};
+
+} // namespace convertible
+
+/**
+ * ByteBufferConvertible is an extensible mechanism for providing
+ * ByteBuffer representations of various data structures and objects.
+ *
+ * ByteBufferConvertible utilizes type erasure and accesses byte buffer data
+ * through the convertible::byte_buffer interface.
+ * Extending ByteBufferConvertible is possible by providing specializations
+ * of convertible::byte_buffer_impl<T> implementing convertible::byte_buffer.
+ */
+class ByteBufferConvertible
+{
+public:
+    ByteBufferConvertible() :
+        m_wrapper(new convertible::byte_buffer_impl<std::nullptr_t>()) {}
+
+    ByteBufferConvertible(std::unique_ptr<convertible::byte_buffer> ptr) :
+        m_wrapper(std::move(ptr)) {}
+
+    template<class T>
+    ByteBufferConvertible(T&& t) :
+        m_wrapper(new convertible::byte_buffer_impl<typename std::decay<T>::type>(std::forward<T>(t))) {}
+
+    ByteBufferConvertible(const ByteBufferConvertible&);
+    ByteBufferConvertible& operator=(const ByteBufferConvertible&);
+
+    ByteBufferConvertible(ByteBufferConvertible&& other) = default;
+    ByteBufferConvertible& operator=(ByteBufferConvertible&& other) = default;
+
+    void convert(ByteBuffer& destination) const { m_wrapper->convert(destination); }
+    std::size_t size() const { return m_wrapper->size(); }
+
+    const convertible::byte_buffer* ptr() const { return m_wrapper.get(); }
+    convertible::byte_buffer* ptr() { return m_wrapper.get(); }
+
+private:
+    std::unique_ptr<convertible::byte_buffer> m_wrapper;
+};
+
+} // namespace vanetza
+
+#endif /* BYTE_BUFFER_CONVERTIBLE_HPP_CFOQNR35 */
+