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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,39 @@
+#include <vanetza/geonet/cbf_packet_identifier.hpp>
+#include <vanetza/geonet/cbf_packet_buffer.hpp>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+CbfPacketIdentifier identifier(const CbfPacket& packet)
+{
+    return identifier(packet.source(), packet.sequence_number());
+}
+
+CbfPacketIdentifier identifier(const Address& source, SequenceNumber sn)
+{
+    return std::make_tuple(source, sn);
+}
+
+} // namespace geonet
+} // namespace vanetza
+
+namespace std
+{
+
+size_t hash<vanetza::geonet::CbfPacketIdentifier>::operator()(const vanetza::geonet::CbfPacketIdentifier& id) const
+{
+    using vanetza::geonet::Address;
+    using vanetza::geonet::SequenceNumber;
+    static_assert(tuple_size<vanetza::geonet::CbfPacketIdentifier>::value == 2, "Unexpected identifier tuple");
+
+    std::size_t seed = 0;
+    const Address& source = get<0>(id);
+    boost::hash_combine(seed, std::hash<Address>()(source));
+    const SequenceNumber& sn = get<1>(id);
+    boost::hash_combine(seed, static_cast<SequenceNumber::value_type>(sn));
+    return seed;
+}
+
+} // namespace std