Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/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