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FLASHING.md says how to take a newer version of the colleague's tree (copy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/security/tests/serialization.hpp

@@ -0,0 +1,73 @@
+#ifndef SERIALIZATION_HPP_ZWGI3RCG
+#define SERIALIZATION_HPP_ZWGI3RCG
+
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/common/byte_buffer_source.hpp>
+#include <vanetza/security/v2/serialization.hpp>
+#include <boost/iostreams/stream_buffer.hpp>
+#include <sstream>
+
+namespace vanetza
+{
+namespace security
+{
+
+/**
+ * \brief create a ByteBuffer from griven hex string
+ * \param string hex string
+ * \return equivalent byte buffer
+ */
+ByteBuffer buffer_from_hexstring(const char*);
+
+/**
+ * \brief Deserialize any class from given hex string
+ * \tparam T the target type of deserialization
+ * \tparam ARGS additional arguments passed to deserialize function
+ * \param string hex string
+ * \param result deserialize into this object
+ * \param args additional arguments for deserialization
+ */
+template<typename T, typename... ARGS>
+size_t deserialize_from_hexstring(const char* string, T& result, ARGS&&... args)
+{
+    auto buffer = buffer_from_hexstring(string);
+    byte_buffer_source source(buffer);
+    boost::iostreams::stream_buffer<byte_buffer_source> stream(source);
+    InputArchive ar(stream);
+    return deserialize(ar, result, std::forward<ARGS>(args)...);
+}
+
+namespace v2
+{
+
+/**
+ * \brief Serialize and deserialize an object
+ *
+ * Source object is serialized and deserialized
+ * object form this binary representation is returned.
+ *
+ * \tparam T the type of the result
+ * \tparam ARGS additional arguments passed to underlying functions
+ * \param source serialize from this object
+ * \param args additional arguments
+ * \return deserialized object (should be equal to source)
+ */
+template<typename T, typename... ARGS>
+T serialize_roundtrip(const T& source, ARGS&&... args)
+{
+    std::stringstream stream;
+    OutputArchive oa(stream);
+    serialize(oa, source, std::forward<ARGS>(args)...);
+
+    T result;
+    InputArchive ia(stream);
+    deserialize(ia, result, std::forward<ARGS>(args)...);
+
+    return result;
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* SERIALIZATION_HPP_ZWGI3RCG */