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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,92 @@
+#ifndef CHUNK_PACKET_HPP_AT4GYSLD
+#define CHUNK_PACKET_HPP_AT4GYSLD
+
+#include <vanetza/common/byte_buffer_convertible.hpp>
+#include <vanetza/net/osi_layer.hpp>
+#include <cstddef>
+#include <map>
+
+namespace vanetza
+{
+
+/**
+ * \brief ChunckPacket is a packet consisting of several memory chunks
+ *
+ * ChunkPacket is the preferred packet type when it is getting assembled step by step.
+ * Each layer can easily add further bytes without caring about other layers at all.
+ */
+class ChunkPacket
+{
+public:
+    ChunkPacket();
+
+    // copy semantics
+    ChunkPacket(const ChunkPacket&);
+    ChunkPacket& operator=(const ChunkPacket&);
+
+    // move semantics
+    ChunkPacket(ChunkPacket&&) = default;
+    ChunkPacket& operator=(ChunkPacket&&) = default;
+
+    /**
+     * Access ByteBufferConvertible of specific layer
+     * \param layer ol Access this layer's data
+     * \return ByteBufferConvertible, might be empty
+     */
+    ByteBufferConvertible& layer(OsiLayer ol);
+    /** \copydoc ChunkPacket::layer */
+    const ByteBufferConvertible& layer(OsiLayer ol) const;
+
+    /** \copydoc ChunkPacket::layer */
+    inline ByteBufferConvertible& operator[](OsiLayer ol)
+    {
+        return layer(ol);
+    }
+
+    /** \copydoc ChunkPacket::layer */
+    inline const ByteBufferConvertible& operator[](OsiLayer ol) const
+    {
+        return layer(ol);
+    }
+
+    /**
+     * Get size of whole payload
+     * \return payload size in bytes
+     */
+    std::size_t size() const;
+
+    /**
+     * Get size of payload from specified layer range
+     * \param from start counting including this layer
+     * \param to stop counting including this layer
+     * \return payload size in bytes
+     */
+    std::size_t size(OsiLayer from, OsiLayer to) const;
+
+    /**
+     * Extract a range of layers from this packet to a new one.
+     * The respective layers of this ChunkPacket are empty afterwards.
+     * \param from start at this layer (inclusive)
+     * \param to stop at this layer (inclusive)
+     * \return new packet containing layers of specified range
+     */
+    ChunkPacket extract(OsiLayer from, OsiLayer to);
+
+    /**
+     * Merge layers from another packet
+     * \param packet source packet (layers will be moved from there)
+     * \param from start at this layer (inclusive)
+     * \param to stop at this layer (inclusive)
+     * \return reference to this packet
+     */
+    ChunkPacket& merge(ChunkPacket& packet, OsiLayer from, OsiLayer to);
+
+private:
+    typedef std::map<OsiLayer, ByteBufferConvertible> map_type;
+    map_type m_layers;
+};
+
+} // namespace vanetza
+
+#endif /* CHUNK_PACKET_HPP_AT4GYSLD */
+