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FLASHING.md says how to take a newer version of the colleague's tree (copy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/security/v3/certificate_cache.cpp

@@ -0,0 +1,59 @@
+#include <vanetza/security/v3/certificate_cache.hpp>
+#include <boost/optional/optional.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v3
+{
+
+const Certificate* CertificateCache::lookup(const HashedId8& digest) const
+{
+    auto found = m_storage.find(digest);
+    if (found != m_storage.end()) {
+        return &found->second;
+    } else {
+        return nullptr;
+    }
+}
+
+const Certificate* CertificateCache::lookup(const HashedId3& digest) const
+{
+    auto found = m_short_digests.find(digest);
+    if (found != m_short_digests.end()) {
+        return &found->second->second;
+    } else {
+        return nullptr;
+    }
+}
+
+void CertificateCache::store(Certificate cert)
+{
+    auto maybe_hash = cert.calculate_digest();
+    if (maybe_hash) {
+        CertificateMap::iterator it;
+        bool inserted;
+        std::tie(it, inserted) = m_storage.emplace(*maybe_hash, std::move(cert));
+        if (inserted) {
+            m_short_digests.emplace(truncate(*maybe_hash), it);
+            m_digests.insert(*maybe_hash);
+        }
+    }
+}
+
+bool CertificateCache::announce(const HashedId8& digest)
+{
+    bool inserted = false;
+    std::tie(std::ignore, inserted) = m_digests.insert(digest);
+    return inserted;
+}
+
+bool CertificateCache::is_known(const HashedId8& digest) const
+{
+    return m_digests.find(digest) != m_digests.end();
+}
+
+} // namespace v3
+} // namespace security
+} // namespace vanetza