Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/asn1/asn1c_conversion.hpp

@@ -0,0 +1,63 @@
+#ifndef ASN1C_CONVERSION_HPP_9E5QN6UC
+#define ASN1C_CONVERSION_HPP_9E5QN6UC
+
+#include <vanetza/asn1/asn1c_wrapper.hpp>
+#include <vanetza/common/byte_buffer_convertible.hpp>
+#include <memory>
+#include <type_traits>
+
+namespace vanetza
+{
+namespace convertible
+{
+
+template<class T>
+struct byte_buffer_impl : public byte_buffer
+{
+public:
+    using wrapper_type = T;
+    static_assert(
+        std::is_base_of<asn1::asn1c_wrapper_common<typename T::asn1c_type>, T>::value,
+        "Only asn1c_wrapper derivates are supported");
+
+    byte_buffer_impl(wrapper_type&& t) :
+        m_wrapper(new wrapper_type(std::move(t)))
+    {
+    }
+
+    byte_buffer_impl(std::shared_ptr<const wrapper_type> other) :
+        m_wrapper(other)
+    {
+    }
+
+    void convert(ByteBuffer& buffer) const override
+    {
+        buffer = m_wrapper->encode();
+    }
+
+    std::unique_ptr<byte_buffer> duplicate() const override
+    {
+        return std::unique_ptr<byte_buffer> {
+            new byte_buffer_impl { m_wrapper }
+        };
+    }
+
+    std::size_t size() const override
+    {
+        return m_wrapper->size();
+    }
+
+    std::shared_ptr<const wrapper_type> wrapper() const
+    {
+        return m_wrapper;
+    }
+
+private:
+    std::shared_ptr<const wrapper_type> m_wrapper;
+};
+
+} // namespace convertible
+} // namespace vanetza
+
+#endif /* ASN1C_CONVERSION_HPP_9E5QN6UC */
+