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/cbf_counter.cpp

@@ -0,0 +1,63 @@
+#include <vanetza/geonet/cbf_counter.hpp>
+#include <cassert>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+void CbfCounterImmortal::add(const id_type& id)
+{
+    ++m_counters[id];
+}
+
+void CbfCounterImmortal::increment(const id_type& id)
+{
+    ++m_counters[id];
+}
+
+auto CbfCounterImmortal::counter(const id_type& id) const -> counter_type
+{
+    counter_type count = 0;
+    auto found = m_counters.find(id);
+    if (found != m_counters.end()) {
+        count = found->second;
+    }
+    return count;
+}
+
+void CbfCounterContending::add(const id_type& id)
+{
+    m_counters[id] = 1;
+}
+
+void CbfCounterContending::remove(const id_type& id)
+{
+    m_counters.erase(id);
+}
+
+CbfCounterFading::CbfCounterFading(Runtime& rt, Clock::duration lifetime) :
+    m_counters(rt)
+{
+    m_counters.set_lifetime(lifetime);
+}
+
+void CbfCounterFading::add(const id_type& id)
+{
+    ++m_counters.refresh(id);
+    m_counters.drop_expired();
+}
+
+void CbfCounterFading::increment(const id_type& id)
+{
+    ++m_counters.get_value(id);
+}
+
+auto CbfCounterFading::counter(const id_type& id) const -> counter_type
+{
+    auto* count = m_counters.get_value_ptr(id);
+    return count ? *count : 0;
+}
+
+} // namespace geonet
+} // namespace vanetza