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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,31 @@
+#include <vanetza/security/v3/revocation_lookup.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v3
+{
+
+void RevocationMemoryLookup::revoke(const HashedId8& issuer, const HashedId8& cert)
+{
+    m_revoked[issuer].insert(cert);
+}
+
+void RevocationMemoryLookup::clear(const HashedId8& issuer)
+{
+    m_revoked.erase(issuer);
+}
+
+bool RevocationMemoryLookup::is_revoked(const HashedId8& issuer, const HashedId8& cert) const
+{
+    auto it = m_revoked.find(issuer);
+    if (it == m_revoked.end()) {
+        return false;
+    }
+    return it->second.count(cert) != 0;
+}
+
+} // namespace v3
+} // namespace security
+} // namespace vanetza