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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,72 @@
+#ifndef GBC_MEMORY_HPP_032N8PRJ
+#define GBC_MEMORY_HPP_032N8PRJ
+
+#include <vanetza/geonet/cbf_packet_identifier.hpp>
+#include <boost/multi_index_container.hpp>
+#include <boost/multi_index/hashed_index.hpp>
+#include <boost/multi_index/sequenced_index.hpp>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+/**
+ * GbcMemory remembers previously seens GBC packets.
+ *
+ * GBC packets are identified by their (GN addr, sequence number) tuple.
+ * The size of GbcMemory is bounded, i.e. it will forget old packets in favour of recent ones.
+ */
+class GbcMemory
+{
+public:
+    using PacketIdentifier = CbfPacketIdentifier;
+
+    /**
+     * Forget a packet if memory exceeds upper limit of stored identifiers
+     * \param num upper limit of remembered packets
+     */
+    void capacity(std::size_t num);
+
+    /**
+     * Number of currently known packets
+     * \return number of packets
+     */
+    std::size_t size() const;
+
+    /**
+     * Remember a particular packet
+     * \param id packet identifier
+     * \return true if packet is already known
+     */
+    bool remember(const PacketIdentifier& id);
+
+    /**
+     * Check if a particular packet is known
+     * \param id packet identifier
+     * \return true if packet is known
+     */
+    bool knows(const PacketIdentifier& id) const;
+
+private:
+    std::size_t m_capacity = 1;
+
+    struct by_packet {};
+    using packet_index = boost::multi_index::hashed_unique<
+        boost::multi_index::tag<by_packet>,
+        boost::multi_index::identity<PacketIdentifier>,
+        std::hash<PacketIdentifier>
+    >;
+    struct by_queue {};
+    using queue_index = boost::multi_index::sequenced<boost::multi_index::tag<by_queue>>;
+
+    using container_type = boost::multi_index_container<PacketIdentifier,
+          boost::multi_index::indexed_by<queue_index, packet_index>>;
+    container_type m_identifiers;
+};
+
+} // namespace geonet
+} // namespace vanetza
+
+#endif /* GBC_MEMORY_HPP_032N8PRJ */
+