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FLASHING.md says how to take a newer version of the colleague's tree (copy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