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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,39 @@
+#include "io_vector.hpp"
+#include "buffer_packet.hpp"
+
+namespace vanetza
+{
+
+void IoVector::clear()
+{
+    m_vector.clear();
+}
+
+void IoVector::append(const void* base, std::size_t length)
+{
+    iovec node;
+    node.iov_base = const_cast<void*>(base);
+    node.iov_len = length;
+    m_vector.push_back(node);
+}
+
+void IoVector::append(const BufferPacket& packet)
+{
+    for (auto& kv : packet) {
+        const ByteBuffer& buffer = kv.second;
+        append(buffer.data(), buffer.size());
+    }
+}
+
+std::size_t IoVector::length() const
+{
+    return m_vector.size();
+}
+
+const iovec* IoVector::base() const
+{
+    return m_vector.empty() ? nullptr : &m_vector[0];
+}
+
+} // namespace vanetza
+