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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,52 @@
+#include <vanetza/geonet/gbc_memory.hpp>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+void GbcMemory::capacity(std::size_t num)
+{
+    m_capacity = num < 1 ? 1 : num;
+
+    // remove excessive identifiers
+    auto& by_queue_index = m_identifiers.get<by_queue>();
+    while (by_queue_index.size() > m_capacity) {
+        by_queue_index.pop_front();
+    }
+}
+
+std::size_t GbcMemory::size() const
+{
+    return m_identifiers.size();
+}
+
+bool GbcMemory::remember(const PacketIdentifier& id)
+{
+    auto& by_packet_index = m_identifiers.get<by_packet>();
+    auto found_packet = by_packet_index.find(id);
+    if (found_packet == by_packet_index.end()) {
+        // make space for one identifier
+        auto& by_queue_index = m_identifiers.get<by_queue>();
+        while (!by_queue_index.empty() && by_queue_index.size() >= m_capacity) {
+            by_queue_index.pop_front();
+        }
+
+        by_queue_index.push_back(id);
+        return false;
+    } else {
+        // packet is already known, just move it to end of queue
+        auto found_queue = m_identifiers.project<by_queue>(found_packet);
+        auto& by_queue_index = m_identifiers.get<by_queue>();
+        by_queue_index.relocate(by_queue_index.end(), found_queue);
+        return true;
+    }
+}
+
+bool GbcMemory::knows(const PacketIdentifier& id) const
+{
+    return m_identifiers.get<by_packet>().find(id) != m_identifiers.get<by_packet>().end();
+}
+
+} // namespace geonet
+} // namespace vanetza