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FLASHING.md says how to take a newer version of the colleague's tree (copy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/common/archives.cpp

@@ -0,0 +1,87 @@
+#include <vanetza/common/archives.hpp>
+
+namespace vanetza
+{
+
+InputArchive::InputArchive(InputStream& is) :
+    m_stream_buffer(is.rdbuf())
+{
+}
+
+InputArchive::InputArchive(StreamBuffer& buf) :
+    m_stream_buffer(&buf)
+{
+}
+
+void InputArchive::load_binary(unsigned char* data, std::size_t len)
+{
+    load_binary(reinterpret_cast<char*>(data), len);
+}
+
+void InputArchive::load_binary(char* data, std::size_t len)
+{
+    std::size_t read_bytes = m_stream_buffer->sgetn(data, len);
+    if (read_bytes != len) {
+        fail(ErrorCode::IncompleteData);
+        throw Exception("incomplete read");
+    }
+}
+
+char InputArchive::peek_byte()
+{
+    auto got = m_stream_buffer->sgetc();
+    if (got == StreamBuffer::traits_type::eof()) {
+        fail(ErrorCode::IncompleteData);
+        throw Exception("impossible peek at end of stream");
+    } else { 
+        return StreamBuffer::traits_type::to_char_type(got);
+    }
+}
+
+bool InputArchive::is_good() const
+{
+    return m_error_code == ErrorCode::Ok;
+}
+
+InputArchive::ErrorCode InputArchive::error_code() const
+{
+    return m_error_code;
+}
+
+void InputArchive::fail(ErrorCode error_code)
+{
+    // do not overwrite prior error code except "ok"
+    if (m_error_code == ErrorCode::Ok) {
+        m_error_code = error_code;
+    }
+}
+
+std::size_t InputArchive::remaining_bytes()
+{
+    return m_stream_buffer->in_avail();
+}
+
+OutputArchive::OutputArchive(OutputStream& os) :
+    m_stream_buffer(os.rdbuf())
+{
+}
+
+OutputArchive::OutputArchive(StreamBuffer& buf) :
+    m_stream_buffer(&buf)
+{
+}
+
+void OutputArchive::save_binary(const unsigned char* data, std::size_t len)
+{
+    save_binary(reinterpret_cast<const char*>(data), len);
+}
+
+void OutputArchive::save_binary(const char* data, std::size_t len)
+{
+    std::size_t written_bytes = m_stream_buffer->sputn(data, len);
+    if (written_bytes != len) {
+        throw Exception("incomplete write");
+    }
+}
+
+} // namespace vanetza